Decoder side intra mode derivation for most probable mode list construction in video coding

ABSTRACT

An method of decoding video data includes deriving, for a current block of video data and using decoder side intra mode derivation (DIMD), a list of intra modes using reconstructed samples of neighboring blocks; constructing, for the current block, a most probable mode (MPM) list, wherein constructing the MPM list comprises inserting, into the MPM list, at least one intra mode from the derived list of intra modes; and predicting, using a candidate selected from the constructed MPM list, the current block.

This application claims the benefit of U.S. Provisional Application No.63/129,004, filed Dec. 22, 2020, the entire contents of which areincorporated by reference herein.

TECHNICAL FIELD

This disclosure relates to video encoding and video decoding.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocoding techniques, such as those described in the standards defined byMPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced VideoCoding (AVC), ITU-T H.265/High Efficiency Video Coding (HEVC), andextensions of such standards. The video devices may transmit, receive,encode, decode, and/or store digital video information more efficientlyby implementing such video coding techniques.

Video coding techniques include spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video picture or a portion of a video picture) maybe partitioned into video blocks, which may also be referred to ascoding tree units (CTUs), coding units (CUs) and/or coding nodes. Videoblocks in an intra-coded (I) slice of a picture are encoded usingspatial prediction with respect to reference samples in neighboringblocks in the same picture. Video blocks in an inter-coded (P or B)slice of a picture may use spatial prediction with respect to referencesamples in neighboring blocks in the same picture or temporal predictionwith respect to reference samples in other reference pictures. Picturesmay be referred to as frames, and reference pictures may be referred toas reference frames.

SUMMARY

In general, this disclosure describes techniques for coding video datausing derived intra mode deviation (DIMD). To perform intra mode codingwithout DIMD, a video coder (e.g., a video encoder and/or a videodecoder) may construct a list of intra mode candidates (e.g., a mostprobable mode (MPM) list) and signal which candidate from the list isused as the intra mode for the current block. To perform intra modecoding with DIMD, a video decoder may implicitly derive intra modes fora current block based on reconstructed samples of neighboring blocks andpredict the current block based on a blending of the derived intramodes. The video encoder may determine whether to predict the currentblock using DIMD or not and signal a syntax element that indicateswhether the current block is predicted using DIMD or predicted using thelist (e.g., not predicted using DIMD). However, implementations of DIMDmay present various disadvantages. For instance, implementations of DIMDprediction may involve a video encoder determining whether to performintra prediction using a blended prediction from a plurality of DIMDderived modes or from a single mode. Such implementations may sacrificerobustness wherein the optimal prediction mode is one of the DIMDderived modes, but optimal prediction might be from a single predictiononly (e.g., as opposed to blended prediction from the DIMD derivedmodes).

In accordance with one or more techniques of this disclosure, a videocoder (e.g., a video encoder and/or a video decoder) may include one ormore of the DIMD derived modes as candidate intra modes in a mostprobable mode (MPM) list. For instance, the video coder may perform DIMDmode derivation to derive one or more DIMD modes and include the one ormore derived DIMD modes in the list of intra mode candidates. The videocoder may signal which candidate from the list is used as the intra modefor the current block. For instance, where a particular DIMD mode one ofthe DIMD modes included in the list is the optimal prediction mode, thevideo encoder may signal that the particular DIMD mode is to be used asthe intra mode for the current block. Use of more optimal modes mayreduce a number of bits used to represent video data. As such, in thisway, the techniques of this disclosure may improve coding efficiency.

In one example, a method of decoding video data includes deriving, for acurrent block of video data and using DIMD, a list of intra modes usingreconstructed samples of neighboring blocks; constructing, for thecurrent block, a most probable mode (MPM) list, wherein constructing theMPM list comprises inserting, into the MPM list, at least one intra modefrom the derived list of intra modes; and predicting, using a candidateselected from the constructed MPM list, the current block.

In another example, a method of encoding includes deriving, for acurrent block of video data and using DIMD, a list of intra modes usingreconstructed samples of neighboring blocks; constructing, for thecurrent block, a MPM list, wherein constructing the MPM list comprisesinserting, into the MPM list, at least one intra mode from the derivedlist of intra modes; selecting, for the current block and from the MPMlist, a candidate intra mode; and encoding, for the current block, oneor more syntax element that specify the candidate intra mode.

In another example, a device for decoding video data includes a memoryconfigured to store video data; and one or more processors implementedin circuitry and configured to: derive, for a current block of videodata and using DIMD, a list of intra modes using reconstructed samplesof neighboring blocks; construct, for the current block, a MPM list,wherein constructing the MPM list comprises inserting, into the MPMlist, at least one intra mode from the derived list of intra modes; andpredict, using a candidate selected from the constructed MPM list, thecurrent block.

In another example, a device for encoding video data includes a memoryconfigured to store video data; and one or more processors implementedin circuitry and configured to: derive, for a current block of videodata and using DIMD, a list of intra modes using reconstructed samplesof neighboring blocks; construct, for the current block, a MPM list,wherein constructing the MPM list comprises inserting, into the MPMlist, at least one intra mode from the derived list of intra modes;select, for the current block and from the MPM list, a candidate intramode; and encode, for the current block, one or more syntax element thatspecify the candidate intra mode.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system that may perform the techniques of this disclosure.

FIGS. 2A and 2B are conceptual diagrams illustrating an example quadtreebinary tree (QTBT) structure, and a corresponding coding tree unit(CTU).

FIG. 3 is a block diagram illustrating an example video encoder that mayperform the techniques of this disclosure.

FIG. 4 is a block diagram illustrating an example video decoder that mayperform the techniques of this disclosure.

FIG. 5 is a conceptual diagram illustrating a set of pixels on which avideo coder may perform a gradient analysis.

FIG. 6 is a graph illustrating an example of orientation index mappingusing horizontal and vertical gradient.

FIG. 7 is a graph illustrating a selection of two most possibleprediction modes.

FIG. 8 is a conceptual diagram illustrating example prediction fordecoder side intra mode derivation (DIMD) mode.

FIG. 9A is a flow diagram illustrating an example technique for intrablock decoding.

FIG. 9B is a flow diagram illustrating an example technique for intrablock decoding with DIMD.

FIG. 10 is a flow diagram illustrating an example technique for intrablock decoding with DIMD most probable mode (MPM) list construction, inaccordance with one or more techniques of this disclosure.

FIG. 11 is a flow diagram illustrating an example technique of MPM listconstruction, in accordance with one or more techniques of thisdisclosure.

FIG. 12 is a flow diagram illustrating an example technique of derivinga list of intra mode by DIMD, in accordance with one or more techniquesof this disclosure.

FIG. 13 is a conceptual diagram illustrating examples of neighboringblocks.

FIG. 14 is a flow diagram illustrating an example technique of addingDIMD derived modes into an MPM list, in accordance with one or moretechniques of this disclosure.

FIG. 15 is a flowchart illustrating an example method for encoding acurrent block in accordance with the techniques of this disclosure.

FIG. 16 is a flowchart illustrating an example method for decoding acurrent block in accordance with the techniques of this disclosure.

FIG. 17 is a flowchart illustrating an example technique for encodingvideo data using DIMD, in accordance with one or more techniques of thisdisclosure.

FIG. 18 is a flowchart illustrating an example technique for decodingvideo data using DIMD, in accordance with one or more techniques of thisdisclosure.

DETAILED DESCRIPTION

Video coding standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-TH.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual(MPEG-4 Part 2), ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC),including its Scalable Video Coding (SVC) and Multiview Video Coding(MVC) extensions, ITU-T H.265 (also known as ISO/IEC MPEG-4 HEVC) withits extensions, and Video Coding (VVC) standardization activity (alsoknown as ITU-T H.266).

In JVET-L0164 “CE3-related: Decoder-side Intra Mode Derivation” JointVideo Experts Team (JVET) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG11, 12th Meeting: Macao, CN, 3-12 Oct. 2018, Document: JVET-L0164(available athttps://jvet-experts.org/doc_end_user/documents/12_Macao/wg11/JVET-L0164-v2.zip),JVET-M0094 “CE3: Decoder-side Intra Mode Derivation (tests 3.1.1,3.1.2,3.1.3 and 3.1.4)” Joint Video Experts Team (JVET) of ITU-T SG 16 WP 3and ISO/IEC JTC 1/SC 29/WG 11, 13th Meeting: Marrakech, MA, 9-18 Jan.2019, Document: JVET-M0094(https://jvet-experts.org/doc_end_user/documents/13_Marrakech/wg11/JVET-M0094-v2.zip), JVET-N0342 “Non-CE3: Decoder-side Intra Mode Derivation withPrediction Fusion” Joint Video Experts Team (JVET) of ITU-T SG 16 WP 3and ISO/IEC JTC 1/SC 29/WG 11, 14th Meeting: Geneva, CH, 19-29 Mar.2019, Document: JVET-N0342(https://jvet-experts.org/doc_end_user/documents/14_Geneva/wg11/JVET-N0342-v5.zip),JVET-00449 “Non-CE3: Decoder-side Intra Mode Derivation with PredictionFusion Using Planar” Joint Video Experts Team (JVET) of ITU-T SG 16 WP 3and ISO/IEC JTC 1/SC 29/WG 11, 15th Meeting: Gothenburg, SE, 3-12 Jul.2019, Document: JVET-00449(https://jvet-experts.org/doc_end_user/documents/15_Gothenburg/wg11/JVET-O0449-v2.zip),decoder side intra mode derivation (DIMD) is proposed as a coding toolfor intra prediction. A difference from existing intra prediction toolsis that, when performing DIMD, a video coder may not explicitly signalintra mode. Instead, the video coder may implicitly derive intra modeusing reconstructed samples of neighboring blocks. The purpose is forcoding efficient improvement by saving signalling of intra mode. Notethat DIMD may only apply to luma. For chroma, classical intra codingmode may apply.

In some examples, to perform DIMD for a current block, a video coder mayperform gradient calculation to derive one or more possible modes (e.g.,M1 and M2). The video coder may then predict the current block usingeach of the derived one or more possible modes to generate intermediateprediction blocks, and generate an output prediction as a function ofthe intermediate prediction blocks. Details of an example DIMD workfloware as follows:

A video coder may perform gradient calculation of reconstructed samplesof neighboring blocks. To derive the intra prediction mode for a block,the video coder may select a set of neighboring pixels from neighboringreconstructed luma samples as shown in FIG. 5. The video coder may thenapply gradient calculation to the center pixel of every 3×3 windowformed by the set of neighboring pixels. Note that if a neighboringpixel is not reconstructed, its gradient values may not be calculated.

The video coder may perform gradient calculation using Sobel filters(denoted as “Mx”, “My”). Dot production between these 2 filters and each3×3 window (denoted as “W”) may be performed to derive horizontal andvertical gradients (denoted as “Gx”, “Gy”) respectively. The followingmay be examples of such filters:

$M_{x} = {{\begin{bmatrix}{- 1} & 0 & 1 \\{- 2} & 0 & 2 \\{- 1} & 0 & 1\end{bmatrix}\mspace{14mu}{and}\mspace{14mu} M_{y}} = \begin{bmatrix}{- 1} & {- 2} & {- 1} \\0 & 0 & 0 \\1 & 2 & 1\end{bmatrix}}$ Gx = M x * W  and  Gy = My * W.

The video coder may map gradient values to a direction. For instance,the video coder may derive the intensity (G) and the orientation (O) foreach window using G_(x) and G_(y):

$G = {{{G_{x}} + {{G_{y}}\mspace{14mu}{and}\mspace{14mu} O}} = {{atan}( \frac{G_{y}}{G_{x}} )}}$

In some examples, to reduce the computational cost of the operationarctangent (“atan”), the orientation may be represented by an indexvalue (in range of 2 to 66) using a mapping table “atan”, and it may beestimated by comparing the mapping table and Gy/Gx; if G_(y)/G_(x) fallsinto the range of (atan[i], atan[i+1]), the orientation is assignedvalue “i”. Note that intensity G is 0, O is assigned to 0 (planar mode)by default. FIG. 6 is a graph illustrating an example of orientationindex mapping using horizontal and vertical gradients.

In the example of FIG. 6, for a given 3×3 window, it (e.g., the indexvalue) satisfies:

angTable[60]<=G _(y) /G _(x)<angTable[61]

The orientation may be mapped to prediction direction 60.

The video coder may perform selection of two most possible modes. Thevideo coder may accumulate the intensity values for each orientationindex of all 3×3 windows. The video coder may select the top twodirections with highest sum as two most possible modes (denote mode ofhighest sum as a first mode “M1” and second highest as a second mode“M2”). Note that If values are all zero, planar mode will be selected.FIG. 7 is a graph illustrating a selection of two most possibleprediction modes. In the example of FIG. 7, the video coder may selectmode 18 at the first mode M1 and mode 24 as the second mode M2 as 18 and24 are, respectively, the first and second highest sums of amplitudes.

The video coder may perform prediction of DIMD. As shown in FIG. 8, ifsum of amplitudes of second most possible mode is 0 (e.g., ifΣamplitude[M2]==0), the video coder may perform normal intra predictionmay be performed with mode M1; otherwise, the video coder may generatean output prediction block as a weighted sum of three prediction blocks(M1, M2, and Planar mode). This may be referred to as performing ablended prediction (e.g., as the modes are blended to generate a singleprediction). As one example, the video coder may generate a weight foreach of the prediction blocks (e.g., ω₁ for M1, ω₂ for M2, and ω₃ forPlanar mode) in accordance with the following equations:

${\omega_{1} = {\frac{43}{64} \times \frac{{ampl}( M_{1} )}{{{ampl}( M_{1} )} + {{ampl}( M_{2} )}}}}{\omega_{2} = {\frac{43}{64} \times \frac{{ampl}( M_{2} )}{{{ampl}( M_{1} )} + {{ampl}( M_{2} )}}}}{\omega_{3} = \frac{21}{64}}$

The video coder may generate intermediate prediction blocks (e.g., Pred₁for M1, Pred₂ for M2, and Pred₃ for Planar mode) based on referencepixels. The video coder may apply the weights to the intermediateprediction blocks to generate the output prediction block in accordancewith the following equation:

Σ_(i=1) ³ω_(i)×Pred_(i)

The video coder may perform signalling of DIMD mode. FIG. 9A is a flowdiagram illustrating an example Intra coding process of VVC, and FIG. 9Bmodifications to the process of FIG. 9A when DIMD is included. As shownin FIG. 9B, a video decoder may parse a DIMD flag. If the DIMD flag istrue (e.g., has a value of 1), the video decoder may derive the intraprediction modes and perform prediction as explained above. If the DIMDflag is false (e.g., has a value of 0), the video decoder may parse theintra prediction mode from the bitstream (e.g., construct a MPM list andsignal an index into the MPM list) and perform prediction accordingly.As such, in the example of FIG. 9B, where the DIMD flag is false, thevideo decoder may not perform DIMD intra mode derivation.

The aforementioned DIMD mechanism may present one or more disadvantages.For instance, the potential of DIMD may not be fully utilized for anumber of reasons. As one example, DIMD prediction implicitly determineswhether the prediction shall be a blended prediction from a plurality ofmodes or from a single mode. The aforementioned DIMD mechanism mightsacrifice robustness wherein the optimal prediction mode is DIMD derivedmode but optimal prediction might be from a single prediction only. Asanother example, in other cases, the optimal intra mode intra mode mightbe different from DIMD derived mode but the difference is small (1 or 2index differences). Using normal mode index coding costs more bits butusing DIMD derived mode does not leads to best RD performance.

In accordance with one or more techniques of this disclosure, a videocoder (e.g., a video encoder and/or a video decoder) may insert DIMDderived modes into a MPM list. As such, a video coder may code a blockusing DIMD derived mode in MPM list for intra prediction.

FIG. 10 is a flow diagram illustrating an example technique for intrablock decoding with DIMD most probable mode (MPM) list construction, inaccordance with one or more techniques of this disclosure. A comparisonof FIGS. 10 and 9B yields several differences. For instance, comparedwith JVET DIMD design (FIG. 9), a video coder performing the techniquesof this disclosure (FIG. 10) may perform DIMD mode derivation regardlesswhether current block is predicted using DIMD mode, and the derivedmodes are added into MPM list (MPM list construction process istherefore postponed after DIMD process).

For blocks with DIMD flag equal to true, the video coder may performDIMD prediction as explained above. For blocks with DIMD flag equal tofalse, the video coder may perform normal intra prediction, and add DIMDderived mode into MPM list. As such, the video coder may use DIMDderived mode for prediction for a block with MPM flag equal to true.

By performing the technique of FIG. 10, a video coder may further extendthe potential of DIMD and may contribute to coding efficiencyimprovement, a block might use DIMD derived mode and perform normalprediction by selecting DIMD derived mode (or DIMD derived mode with anoffset) in MPM list.

FIG. 11 is a flow diagram illustrating an example technique of MPM listconstruction/derivation, in accordance with one or more techniques ofthis disclosure. The techniques of FIG. 11 may be performed by a videocoder, such as video encoder 200 and/or video decoder 300.

As shown in FIG. 11, in step 1 (1102), the video coder may derive a listof intra modes using reconstructed samples of neighboring blocks byDIMD. In step 2 (1104), the video coder may add prediction modes fromneighboring blocks into MPM list. In step 3 (1106), the video coder mayadd the list of intra modes derived by DIMD into MPM list. In step 4(1108), the video coder may add more candidates into MPM list using thelist of candidates. An example method is to add a plurality of offsets(in range of −3 to 3) to all the candidates in the list, or some of thecandidates in the list (for example, first 3 candidates). In step 5(1110), the video coder may add default intra modes (DC, planar,horizontal, vertical etc. modes) into MPM list (e.g., insert

As such, steps 4 and/or 5 of FIG. 11 illustrates steps in which thevideo coder may insert, into the MPM list and after the at least oneintra mode from the derived list of intra modes, additional intra modecandidates, which may be one or more default candidates. Additionally oralternatively, step 2 may illustrate a step in which the video coder mayinsert into the MPM list and before the at least one intra mode from thederived list of intra modes, one or more intra mode candidates that areprediction modes from neighboring blocks of the current block.

FIG. 12 is a flow diagram illustrating an example technique of derivinga list of intra mode by DIMD, in accordance with one or more techniquesof this disclosure. The techniques of FIG. 12 may be performed by avideo coder, such as video encoder 200 and/or video decoder 300. Thetechnique of FIG. 12 may be an example of step 1 (1102) of the techniqueof FIG. 11.

In 1202, the video coder may calculate horizontal and vertical gradientvalues of each window of neighboring blocks as Gx and Gy. FIG. 5illustrates an example window. In 1204, for each set of horizontal andvertical gradient values, the video coder may derive the intensity(|Gx|+|Gy|) and orientation values (Gy/Gx) and map each orientation toan intra mode in range of 2 to 66 (example process is given above). Thevideo coder may also calculate the intensity value as sum of absolutevalues of horizontal and vertical gradient values, the intensity valuemay also be calculated as sum of square values of horizontal andvertical gradient values. In 1206, for each intra mode, the video codermay accumulate its corresponding intensity values. In 1208, the videocoder may sort the intra modes according to the accumulated intensityvalues from high to low. The DIMD list may be the sorted list of intramodes, or only contain partial of the list. The DIMD list can excludeintra modes with sum of intensity values equal to 0. The DIMD list canexclude intra modes with sum of intensity values less than a threshold.The size of the list can be 0, 1, 2, or more. The first candidate can beset to DC or planar mode if all sum of intensity values are 0.

As shown above in FIG. 11, in 1104, the video coder may add intraprediction modes of neighboring blocks into MPM lists. Exampleneighboring blocks are left, above, above left, above right and belowleft blocks as shown in FIG. 13

FIG. 14 is a flow diagram illustrating an example technique of addingDIMD derived modes into MPM list, in accordance with one or moretechniques of this disclosure. The techniques of FIG. 14 may beperformed by a video coder, such as video encoder 200 and/or videodecoder 300. The technique of FIG. 14 may be an example of step 3 of thetechnique of FIG. 11.

In 1402, the video coder may add the first candidate with highest sum ofintensity (denoted as “M1” as explained above) into MPM list. In 1404,the video coder may determine whether the second candidate's sum ofintensity is 0 (denoted as “M2” as explained above), if it is determinedto be 0, the second candidate may be skipped; otherwise, 1406 will beperformed. In 1406, the video coder may add the second candidate intoMPM list.

Some example variations and/or alternatives follow:

-   1) In 1404, the video coder may determine whether the second    candidate's sum of intensity is less than a threshold. If it is less    than a threshold, the video coder may skip the second candidate;    otherwise, the video coder may add the second candidate into MPM    list construction.-   2) 1404 condition may also be applied to the first candidate.-   3) The order of the technique of FIG. 11 may be switched with each    other or in an interleaved way. For example, 1106 may be performed    before 1104, or DIMD derived modes and intra modes from neighboring    blocks may be added in an interleaved way.-   4) When a coder performs 1104 before 1102, the list of intra modes    derived by DIMD may be pruned by intra modes from neighboring    blocks; For example, if an intra mode has already been added into    MPM list in 1104, the intra mode may be skipped when building the    list of intra modes of DIMD lists.-   5) In 4) if an intra mode has already been added into MPM list in    1104, any mode that equals to the intra mode plus an offset (the    offset value may be from −3 to 3) will be skipped when building the    list of intra modes of DIMD lists.-   6) The list of intra modes derived by DIMD may also be sorted in a    different order (for example, sum of intensity value from low to    high and keep last few candidates)-   7) Each candidate added into MPM list may be pruned to avoid    duplicate modes added into MPM list.-   8) The first candidate may be skipped if it is equal to DC or planar    mode.

Some other example variations and/or alternatives follow:

-   1) DIMD flag may be signaled after MPM flag-   2) DIMD flag may be signaled as one of MPM index-   3) There may be only one mode derived by DIMD that is added into MPM    list-   4) There may be more than 2 modes derived by DIMD that are added    into MPM list-   5) DIMD may also be applied to chroma block-   6) DIMD derived mode may also be added into chroma MPM list-   7) Intra prediction might always use a single prediction mode-   8) In the case of 7) DIMD flag might not be signalled-   9) DIMD prediction might only uses a single mode-   10) DIMD prediction might be a blended prediction of a derived mode    and planar mode-   11) DIMD prediction might be a blended prediction of derive mode(s)    and DC mode-   12) DIMD may use prediction sample instead of reconstructed samples    for mode derivation-   13) If a block is of DIMD mode, its prediction mode derived by DIMD    may be used for MPM list construction of neighboring blocks.-   14) If a block is of DIMD mode, a default mode (DC or planar) may be    used for MPM list construction of neighboring blocks.

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system 100 that may perform the techniques of this disclosure.The techniques of this disclosure are generally directed to coding(encoding and/or decoding) video data. In general, video data includesany data for processing a video. Thus, video data may include raw,unencoded video, encoded video, decoded (e.g., reconstructed) video, andvideo metadata, such as signaling data.

As shown in FIG. 1, system 100 includes a source device 102 thatprovides encoded video data to be decoded and displayed by a destinationdevice 116, in this example. In particular, source device 102 providesthe video data to destination device 116 via a computer-readable medium110. Source device 102 and destination device 116 may comprise any of awide range of devices, including desktop computers, notebook (i.e.,laptop) computers, mobile devices, tablet computers, set-top boxes,telephone handsets such as smartphones, televisions, cameras, displaydevices, digital media players, video gaming consoles, video streamingdevice, broadcast receiver devices, or the like. In some cases, sourcedevice 102 and destination device 116 may be equipped for wirelesscommunication, and thus may be referred to as wireless communicationdevices.

In the example of FIG. 1, source device 102 includes video source 104,memory 106, video encoder 200, and output interface 108. Destinationdevice 116 includes input interface 122, video decoder 300, memory 120,and display device 118. In accordance with this disclosure, videoencoder 200 of source device 102 and video decoder 300 of destinationdevice 116 may be configured to apply the techniques for intra modederivation for most probably mode list construction. Thus, source device102 represents an example of a video encoding device, while destinationdevice 116 represents an example of a video decoding device. In otherexamples, a source device and a destination device may include othercomponents or arrangements. For example, source device 102 may receivevideo data from an external video source, such as an external camera.Likewise, destination device 116 may interface with an external displaydevice, rather than include an integrated display device.

System 100 as shown in FIG. 1 is merely one example. In general, anydigital video encoding and/or decoding device may perform techniques forintra mode derivation for most probably mode list construction. Sourcedevice 102 and destination device 116 are merely examples of such codingdevices in which source device 102 generates coded video data fortransmission to destination device 116. This disclosure refers to a“coding” device as a device that performs coding (encoding and/ordecoding) of data. Thus, video encoder 200 and video decoder 300represent examples of coding devices, in particular, a video encoder anda video decoder, respectively. In some examples, source device 102 anddestination device 116 may operate in a substantially symmetrical mannersuch that each of source device 102 and destination device 116 includesvideo encoding and decoding components. Hence, system 100 may supportone-way or two-way video transmission between source device 102 anddestination device 116, e.g., for video streaming, video playback, videobroadcasting, or video telephony.

In general, video source 104 represents a source of video data (i.e.,raw, unencoded video data) and provides a sequential series of pictures(also referred to as “frames”) of the video data to video encoder 200,which encodes data for the pictures. Video source 104 of source device102 may include a video capture device, such as a video camera, a videoarchive containing previously captured raw video, and/or a video feedinterface to receive video from a video content provider. As a furtheralternative, video source 104 may generate computer graphics-based dataas the source video, or a combination of live video, archived video, andcomputer-generated video. In each case, video encoder 200 encodes thecaptured, pre-captured, or computer-generated video data. Video encoder200 may rearrange the pictures from the received order (sometimesreferred to as “display order”) into a coding order for coding. Videoencoder 200 may generate a bitstream including encoded video data.Source device 102 may then output the encoded video data via outputinterface 108 onto computer-readable medium 110 for reception and/orretrieval by, e.g., input interface 122 of destination device 116.

Memory 106 of source device 102 and memory 120 of destination device 116represent general purpose memories. In some examples, memories 106, 120may store raw video data, e.g., raw video from video source 104 and raw,decoded video data from video decoder 300. Additionally oralternatively, memories 106, 120 may store software instructionsexecutable by, e.g., video encoder 200 and video decoder 300,respectively. Although memory 106 and memory 120 are shown separatelyfrom video encoder 200 and video decoder 300 in this example, it shouldbe understood that video encoder 200 and video decoder 300 may alsoinclude internal memories for functionally similar or equivalentpurposes. Furthermore, memories 106, 120 may store encoded video data,e.g., output from video encoder 200 and input to video decoder 300. Insome examples, portions of memories 106, 120 may be allocated as one ormore video buffers, e.g., to store raw, decoded, and/or encoded videodata.

Computer-readable medium 110 may represent any type of medium or devicecapable of transporting the encoded video data from source device 102 todestination device 116. In one example, computer-readable medium 110represents a communication medium to enable source device 102 totransmit encoded video data directly to destination device 116 inreal-time, e.g., via a radio frequency network or computer-basednetwork. Output interface 108 may modulate a transmission signalincluding the encoded video data, and input interface 122 may demodulatethe received transmission signal, according to a communication standard,such as a wireless communication protocol. The communication medium maycomprise any wireless or wired communication medium, such as a radiofrequency (RF) spectrum or one or more physical transmission lines. Thecommunication medium may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network such as theInternet. The communication medium may include routers, switches, basestations, or any other equipment that may be useful to facilitatecommunication from source device 102 to destination device 116.

In some examples, source device 102 may output encoded data from outputinterface 108 to storage device 112. Similarly, destination device 116may access encoded data from storage device 112 via input interface 122.Storage device 112 may include any of a variety of distributed orlocally accessed data storage media such as a hard drive, Blu-ray discs,DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or anyother suitable digital storage media for storing encoded video data.

In some examples, source device 102 may output encoded video data tofile server 114 or another intermediate storage device that may storethe encoded video data generated by source device 102. Destinationdevice 116 may access stored video data from file server 114 viastreaming or download.

File server 114 may be any type of server device capable of storingencoded video data and transmitting that encoded video data to thedestination device 116. File server 114 may represent a web server(e.g., for a website), a server configured to provide a file transferprotocol service (such as File Transfer Protocol (FTP) or File Deliveryover Unidirectional Transport (FLUTE) protocol), a content deliverynetwork (CDN) device, a hypertext transfer protocol (HTTP) server, aMultimedia Broadcast Multicast Service (MBMS) or Enhanced MBMS (eMBMS)server, and/or a network attached storage (NAS) device. File server 114may, additionally or alternatively, implement one or more HTTP streamingprotocols, such as Dynamic Adaptive Streaming over HTTP (DASH), HTTPLive Streaming (HLS), Real Time Streaming Protocol (RTSP), HTTP DynamicStreaming, or the like.

Destination device 116 may access encoded video data from file server114 through any standard data connection, including an Internetconnection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., digital subscriber line (DSL),cable modem, etc.), or a combination of both that is suitable foraccessing encoded video data stored on file server 114. Input interface122 may be configured to operate according to any one or more of thevarious protocols discussed above for retrieving or receiving media datafrom file server 114, or other such protocols for retrieving media data.

Output interface 108 and input interface 122 may represent wirelesstransmitters/receivers, modems, wired networking components (e.g.,Ethernet cards), wireless communication components that operateaccording to any of a variety of IEEE 802.11 standards, or otherphysical components. In examples where output interface 108 and inputinterface 122 comprise wireless components, output interface 108 andinput interface 122 may be configured to transfer data, such as encodedvideo data, according to a cellular communication standard, such as 4G,4G-LTE (Long-Term Evolution), LTE Advanced, 5G, or the like. In someexamples where output interface 108 comprises a wireless transmitter,output interface 108 and input interface 122 may be configured totransfer data, such as encoded video data, according to other wirelessstandards, such as an IEEE 802.11 specification, an IEEE 802.15specification (e.g., ZigBee™), a Bluetooth™ standard, or the like. Insome examples, source device 102 and/or destination device 116 mayinclude respective system-on-a-chip (SoC) devices. For example, sourcedevice 102 may include an SoC device to perform the functionalityattributed to video encoder 200 and/or output interface 108, anddestination device 116 may include an SoC device to perform thefunctionality attributed to video decoder 300 and/or input interface122.

The techniques of this disclosure may be applied to video coding insupport of any of a variety of multimedia applications, such asover-the-air television broadcasts, cable television transmissions,satellite television transmissions, Internet streaming videotransmissions, such as dynamic adaptive streaming over HTTP (DASH),digital video that is encoded onto a data storage medium, decoding ofdigital video stored on a data storage medium, or other applications.

Input interface 122 of destination device 116 receives an encoded videobitstream from computer-readable medium 110 (e.g., a communicationmedium, storage device 112, file server 114, or the like). The encodedvideo bitstream may include signaling information defined by videoencoder 200, which is also used by video decoder 300, such as syntaxelements having values that describe characteristics and/or processingof video blocks or other coded units (e.g., slices, pictures, groups ofpictures, sequences, or the like). Display device 118 displays decodedpictures of the decoded video data to a user. Display device 118 mayrepresent any of a variety of display devices such as a liquid crystaldisplay (LCD), a plasma display, an organic light emitting diode (OLED)display, or another type of display device.

Although not shown in FIG. 1, in some examples, video encoder 200 andvideo decoder 300 may each be integrated with an audio encoder and/oraudio decoder, and may include appropriate MUX-DEMUX units, or otherhardware and/or software, to handle multiplexed streams including bothaudio and video in a common data stream. If applicable, MUX-DEMUX unitsmay conform to the ITU H.223 multiplexer protocol, or other protocolssuch as the user datagram protocol (UDP).

Video encoder 200 and video decoder 300 each may be implemented as anyof a variety of suitable encoder and/or decoder circuitry, such as oneor more microprocessors, digital signal processors (DSPs), applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs), discrete logic, software, hardware, firmware or anycombinations thereof. When the techniques are implemented partially insoftware, a device may store instructions for the software in asuitable, non-transitory computer-readable medium and execute theinstructions in hardware using one or more processors to perform thetechniques of this disclosure. Each of video encoder 200 and videodecoder 300 may be included in one or more encoders or decoders, eitherof which may be integrated as part of a combined encoder/decoder (CODEC)in a respective device. A device including video encoder 200 and/orvideo decoder 300 may comprise an integrated circuit, a microprocessor,and/or a wireless communication device, such as a cellular telephone.

Video encoder 200 and video decoder 300 may operate according to a videocoding standard, such as ITU-T H.265, also referred to as HighEfficiency Video Coding (HEVC) or extensions thereto, such as themulti-view and/or scalable video coding extensions. Alternatively, videoencoder 200 and video decoder 300 may operate according to otherproprietary or industry standards, such as ITU-T H.266, also referred toas Versatile Video Coding (VVC). A draft of the VVC standard isdescribed in Bross, et al. “Versatile Video Coding (Draft 10),” JointVideo Experts Team (JVET) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG11, 20^(th) Meeting: by teleconference, 7-16 Oct. 2020, JVET-T2001-v2(hereinafter “VVC Draft 10”). The techniques of this disclosure,however, are not limited to any particular coding standard.

In general, video encoder 200 and video decoder 300 may performblock-based coding of pictures. The term “block” generally refers to astructure including data to be processed (e.g., encoded, decoded, orotherwise used in the encoding and/or decoding process). For example, ablock may include a two-dimensional matrix of samples of luminanceand/or chrominance data. In general, video encoder 200 and video decoder300 may code video data represented in a YUV (e.g., Y, Cb, Cr) format.That is, rather than coding red, green, and blue (RGB) data for samplesof a picture, video encoder 200 and video decoder 300 may code luminanceand chrominance components, where the chrominance components may includeboth red hue and blue hue chrominance components. In some examples,video encoder 200 converts received RGB formatted data to a YUVrepresentation prior to encoding, and video decoder 300 converts the YUVrepresentation to the RGB format. Alternatively, pre- andpost-processing units (not shown) may perform these conversions.

This disclosure may generally refer to coding (e.g., encoding anddecoding) of pictures to include the process of encoding or decodingdata of the picture. Similarly, this disclosure may refer to coding ofblocks of a picture to include the process of encoding or decoding datafor the blocks, e.g., prediction and/or residual coding. An encodedvideo bitstream generally includes a series of values for syntaxelements representative of coding decisions (e.g., coding modes) andpartitioning of pictures into blocks. Thus, references to coding apicture or a block should generally be understood as coding values forsyntax elements forming the picture or block.

HEVC defines various blocks, including coding units (CUs), predictionunits (PUs), and transform units (TUs). According to HEVC, a video coder(such as video encoder 200) partitions a coding tree unit (CTU) into CUsaccording to a quadtree structure. That is, the video coder partitionsCTUs and CUs into four equal, non-overlapping squares, and each node ofthe quadtree has either zero or four child nodes. Nodes without childnodes may be referred to as “leaf nodes,” and CUs of such leaf nodes mayinclude one or more PUs and/or one or more TUs. The video coder mayfurther partition PUs and TUs. For example, in HEVC, a residual quadtree(RQT) represents partitioning of TUs. In HEVC, PUs representinter-prediction data, while TUs represent residual data. CUs that areintra-predicted include intra-prediction information, such as anintra-mode indication.

As another example, video encoder 200 and video decoder 300 may beconfigured to operate according to VVC. According to VVC, a video coder(such as video encoder 200) partitions a picture into a plurality ofcoding tree units (CTUs). Video encoder 200 may partition a CTUaccording to a tree structure, such as a quadtree-binary tree (QTBT)structure or Multi-Type Tree (MTT) structure. The QTBT structure removesthe concepts of multiple partition types, such as the separation betweenCUs, PUs, and TUs of HEVC. A QTBT structure includes two levels: a firstlevel partitioned according to quadtree partitioning, and a second levelpartitioned according to binary tree partitioning. A root node of theQTBT structure corresponds to a CTU. Leaf nodes of the binary treescorrespond to coding units (CUs).

In an MTT partitioning structure, blocks may be partitioned using aquadtree (QT) partition, a binary tree (BT) partition, and one or moretypes of triple tree (TT) (also called ternary tree (TT)) partitions. Atriple or ternary tree partition is a partition where a block is splitinto three sub-blocks. In some examples, a triple or ternary treepartition divides a block into three sub-blocks without dividing theoriginal block through the center. The partitioning types in MTT (e.g.,QT, BT, and TT), may be symmetrical or asymmetrical.

In some examples, video encoder 200 and video decoder 300 may use asingle QTBT or MTT structure to represent each of the luminance andchrominance components, while in other examples, video encoder 200 andvideo decoder 300 may use two or more QTBT or MTT structures, such asone QTBT/MTT structure for the luminance component and another QTBT/MTTstructure for both chrominance components (or two QTBT/MTT structuresfor respective chrominance components).

Video encoder 200 and video decoder 300 may be configured to usequadtree partitioning per HEVC, QTBT partitioning, MTT partitioning, orother partitioning structures. For purposes of explanation, thedescription of the techniques of this disclosure is presented withrespect to QTBT partitioning. However, it should be understood that thetechniques of this disclosure may also be applied to video codersconfigured to use quadtree partitioning, or other types of partitioningas well.

In some examples, a CTU includes a coding tree block (CTB) of lumasamples, two corresponding CTBs of chroma samples of a picture that hasthree sample arrays, or a CTB of samples of a monochrome picture or apicture that is coded using three separate color planes and syntaxstructures used to code the samples. A CTB may be an N×N block ofsamples for some value of N such that the division of a component intoCTBs is a partitioning. A component is an array or single sample fromone of the three arrays (luma and two chroma) that compose a picture in4:2:0, 4:2:2, or 4:4:4 color format or the array or a single sample ofthe array that compose a picture in monochrome format. In some examples,a coding block is an M×N block of samples for some values of M and Nsuch that a division of a CTB into coding blocks is a partitioning.

The blocks (e.g., CTUs or CUs) may be grouped in various ways in apicture. As one example, a brick may refer to a rectangular region ofCTU rows within a particular tile in a picture. A tile may be arectangular region of CTUs within a particular tile column and aparticular tile row in a picture. A tile column refers to a rectangularregion of CTUs having a height equal to the height of the picture and awidth specified by syntax elements (e.g., such as in a picture parameterset). A tile row refers to a rectangular region of CTUs having a heightspecified by syntax elements (e.g., such as in a picture parameter set)and a width equal to the width of the picture.

In some examples, a tile may be partitioned into multiple bricks, eachof which may include one or more CTU rows within the tile. A tile thatis not partitioned into multiple bricks may also be referred to as abrick. However, a brick that is a true subset of a tile may not bereferred to as a tile.

The bricks in a picture may also be arranged in a slice. A slice may bean integer number of bricks of a picture that may be exclusivelycontained in a single network abstraction layer (NAL) unit. In someexamples, a slice includes either a number of complete tiles or only aconsecutive sequence of complete bricks of one tile.

This disclosure may use “N×N” and “N by N” interchangeably to refer tothe sample dimensions of a block (such as a CU or other video block) interms of vertical and horizontal dimensions, e.g., 16×16 samples or 16by 16 samples. In general, a 16×16 CU will have 16 samples in a verticaldirection (y=16) and 16 samples in a horizontal direction (x=16).Likewise, an N×N CU generally has N samples in a vertical direction andN samples in a horizontal direction, where N represents a nonnegativeinteger value. The samples in a CU may be arranged in rows and columns.Moreover, CUs need not necessarily have the same number of samples inthe horizontal direction as in the vertical direction. For example, CUsmay comprise N×M samples, where M is not necessarily equal to N.

Video encoder 200 encodes video data for CUs representing predictionand/or residual information, and other information. The predictioninformation indicates how the CU is to be predicted in order to form aprediction block for the CU. The residual information generallyrepresents sample-by-sample differences between samples of the CU priorto encoding and the prediction block.

To predict a CU, video encoder 200 may generally form a prediction blockfor the CU through inter-prediction or intra-prediction.Inter-prediction generally refers to predicting the CU from data of apreviously coded picture, whereas intra-prediction generally refers topredicting the CU from previously coded data of the same picture. Toperform inter-prediction, video encoder 200 may generate the predictionblock using one or more motion vectors. Video encoder 200 may generallyperform a motion search to identify a reference block that closelymatches the CU, e.g., in terms of differences between the CU and thereference block. Video encoder 200 may calculate a difference metricusing a sum of absolute difference (SAD), sum of squared differences(SSD), mean absolute difference (MAD), mean squared differences (MSD),or other such difference calculations to determine whether a referenceblock closely matches the current CU. In some examples, video encoder200 may predict the current CU using uni-directional prediction orbi-directional prediction.

Some examples of VVC also provide an affine motion compensation mode,which may be considered an inter-prediction mode. In affine motioncompensation mode, video encoder 200 may determine two or more motionvectors that represent non-translational motion, such as zoom in or out,rotation, perspective motion, or other irregular motion types.

To perform intra-prediction, video encoder 200 may select anintra-prediction mode to generate the prediction block. Some examples ofVVC provide sixty-seven intra-prediction modes, including variousdirectional modes, as well as planar mode and DC mode. In general, videoencoder 200 selects an intra-prediction mode that describes neighboringsamples to a current block (e.g., a block of a CU) from which to predictsamples of the current block. Such samples may generally be above, aboveand to the left, or to the left of the current block in the same pictureas the current block, assuming video encoder 200 codes CTUs and CUs inraster scan order (left to right, top to bottom).

Video encoder 200 encodes data representing the prediction mode for acurrent block. For example, for inter-prediction modes, video encoder200 may encode data representing which of the various availableinter-prediction modes is used, as well as motion information for thecorresponding mode. For uni-directional or bi-directionalinter-prediction, for example, video encoder 200 may encode motionvectors using advanced motion vector prediction (AMVP) or merge mode.Video encoder 200 may use similar modes to encode motion vectors foraffine motion compensation mode.

Following prediction, such as intra-prediction or inter-prediction of ablock, video encoder 200 may calculate residual data for the block. Theresidual data, such as a residual block, represents sample by sampledifferences between the block and a prediction block for the block,formed using the corresponding prediction mode. Video encoder 200 mayapply one or more transforms to the residual block, to producetransformed data in a transform domain instead of the sample domain. Forexample, video encoder 200 may apply a discrete cosine transform (DCT),an integer transform, a wavelet transform, or a conceptually similartransform to residual video data. Additionally, video encoder 200 mayapply a secondary transform following the first transform, such as amode-dependent non-separable secondary transform (MDNSST), a signaldependent transform, a Karhunen-Loeve transform (KLT), or the like.Video encoder 200 produces transform coefficients following applicationof the one or more transforms.

As noted above, following any transforms to produce transformcoefficients, video encoder 200 may perform quantization of thetransform coefficients. Quantization generally refers to a process inwhich transform coefficients are quantized to possibly reduce the amountof data used to represent the transform coefficients, providing furthercompression. By performing the quantization process, video encoder 200may reduce the bit depth associated with some or all of the transformcoefficients. For example, video encoder 200 may round an n-bit valuedown to an m-bit value during quantization, where n is greater than m.In some examples, to perform quantization, video encoder 200 may performa bitwise right-shift of the value to be quantized.

Following quantization, video encoder 200 may scan the transformcoefficients, producing a one-dimensional vector from thetwo-dimensional matrix including the quantized transform coefficients.The scan may be designed to place higher energy (and therefore lowerfrequency) transform coefficients at the front of the vector and toplace lower energy (and therefore higher frequency) transformcoefficients at the back of the vector. In some examples, video encoder200 may utilize a predefined scan order to scan the quantized transformcoefficients to produce a serialized vector, and then entropy encode thequantized transform coefficients of the vector. In other examples, videoencoder 200 may perform an adaptive scan. After scanning the quantizedtransform coefficients to form the one-dimensional vector, video encoder200 may entropy encode the one-dimensional vector, e.g., according tocontext-adaptive binary arithmetic coding (CABAC). Video encoder 200 mayalso entropy encode values for syntax elements describing metadataassociated with the encoded video data for use by video decoder 300 indecoding the video data.

To perform CABAC, video encoder 200 may assign a context within acontext model to a symbol to be transmitted. The context may relate to,for example, whether neighboring values of the symbol are zero-valued ornot. The probability determination may be based on a context assigned tothe symbol.

Video encoder 200 may further generate syntax data, such as block-basedsyntax data, picture-based syntax data, and sequence-based syntax data,to video decoder 300, e.g., in a picture header, a block header, a sliceheader, or other syntax data, such as a sequence parameter set (SPS),picture parameter set (PPS), or video parameter set (VPS). Video decoder300 may likewise decode such syntax data to determine how to decodecorresponding video data.

In this manner, video encoder 200 may generate a bitstream includingencoded video data, e.g., syntax elements describing partitioning of apicture into blocks (e.g., CUs) and prediction and/or residualinformation for the blocks. Ultimately, video decoder 300 may receivethe bitstream and decode the encoded video data.

In general, video decoder 300 performs a reciprocal process to thatperformed by video encoder 200 to decode the encoded video data of thebitstream. For example, video decoder 300 may decode values for syntaxelements of the bitstream using CABAC in a manner substantially similarto, albeit reciprocal to, the CABAC encoding process of video encoder200. The syntax elements may define partitioning information forpartitioning of a picture into CTUs, and partitioning of each CTUaccording to a corresponding partition structure, such as a QTBTstructure, to define CUs of the CTU. The syntax elements may furtherdefine prediction and residual information for blocks (e.g., CUs) ofvideo data.

The residual information may be represented by, for example, quantizedtransform coefficients. Video decoder 300 may inverse quantize andinverse transform the quantized transform coefficients of a block toreproduce a residual block for the block. Video decoder 300 uses asignaled prediction mode (intra- or inter-prediction) and relatedprediction information (e.g., motion information for inter-prediction)to form a prediction block for the block. Video decoder 300 may thencombine the prediction block and the residual block (on asample-by-sample basis) to reproduce the original block. Video decoder300 may perform additional processing, such as performing a deblockingprocess to reduce visual artifacts along boundaries of the block.

In accordance with one or more techniques of this disclosure, a videocoder (e.g., a video encoder and/or a video decoder) may insert DIMDderived modes into a MPM list. As such, a video coder may code a blockusing DIMD derived mode in MPM list for intra prediction.

This disclosure may generally refer to “signaling” certain information,such as syntax elements. The term “signaling” may generally refer to thecommunication of values for syntax elements and/or other data used todecode encoded video data. That is, video encoder 200 may signal valuesfor syntax elements in the bitstream. In general, signaling refers togenerating a value in the bitstream. As noted above, source device 102may transport the bitstream to destination device 116 substantially inreal time, or not in real time, such as might occur when storing syntaxelements to storage device 112 for later retrieval by destination device116.

In accordance with one or more techniques of this disclosure, encoder200 and/or decoder 300 may insert one or more derived DIMD modes into anMPM list. For instance, encoder 200 and/or decoder 300 may perform thetechnique of FIG. 10.

FIGS. 2A and 2B are conceptual diagrams illustrating an example quadtreebinary tree (QTBT) structure 130, and a corresponding coding tree unit(CTU) 132. The solid lines represent quadtree splitting, and dottedlines indicate binary tree splitting. In each split (i.e., non-leaf)node of the binary tree, one flag is signaled to indicate whichsplitting type (i.e., horizontal or vertical) is used, where 0 indicateshorizontal splitting and 1 indicates vertical splitting in this example.For the quadtree splitting, there is no need to indicate the splittingtype, because quadtree nodes split a block horizontally and verticallyinto 4 sub-blocks with equal size. Accordingly, video encoder 200 mayencode, and video decoder 300 may decode, syntax elements (such assplitting information) for a region tree level of QTBT structure 130(i.e., the solid lines) and syntax elements (such as splittinginformation) for a prediction tree level of QTBT structure 130 (i.e.,the dashed lines). Video encoder 200 may encode, and video decoder 300may decode, video data, such as prediction and transform data, for CUsrepresented by terminal leaf nodes of QTBT structure 130.

In general, CTU 132 of FIG. 2B may be associated with parametersdefining sizes of blocks corresponding to nodes of QTBT structure 130 atthe first and second levels. These parameters may include a CTU size(representing a size of CTU 132 in samples), a minimum quadtree size(MinQTSize, representing a minimum allowed quadtree leaf node size), amaximum binary tree size (MaxBTSize, representing a maximum allowedbinary tree root node size), a maximum binary tree depth (MaxBTDepth,representing a maximum allowed binary tree depth), and a minimum binarytree size (MinBTSize, representing the minimum allowed binary tree leafnode size).

The root node of a QTBT structure corresponding to a CTU may have fourchild nodes at the first level of the QTBT structure, each of which maybe partitioned according to quadtree partitioning. That is, nodes of thefirst level are either leaf nodes (having no child nodes) or have fourchild nodes. The example of QTBT structure 130 represents such nodes asincluding the parent node and child nodes having solid lines forbranches. If nodes of the first level are not larger than the maximumallowed binary tree root node size (MaxBTSize), then the nodes can befurther partitioned by respective binary trees. The binary treesplitting of one node can be iterated until the nodes resulting from thesplit reach the minimum allowed binary tree leaf node size (MinBTSize)or the maximum allowed binary tree depth (MaxBTDepth). The example ofQTBT structure 130 represents such nodes as having dashed lines forbranches. The binary tree leaf node is referred to as a coding unit(CU), which is used for prediction (e.g., intra-picture or inter-pictureprediction) and transform, without any further partitioning. Asdiscussed above, CUs may also be referred to as “video blocks” or“blocks.”

In one example of the QTBT partitioning structure, the CTU size is setas 128×128 (luma samples and two corresponding 64×64 chroma samples),the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64, theMinBTSize (for both width and height) is set as 4, and the MaxBTDepth isset as 4. The quadtree partitioning is applied to the CTU first togenerate quad-tree leaf nodes. The quadtree leaf nodes may have a sizefrom 16×16 (i.e., the MinQTSize) to 128×128 (i.e., the CTU size). If thequadtree leaf node is 128×128, the leaf quadtree node will not befurther split by the binary tree, because the size exceeds the MaxBTSize(i.e., 64×64, in this example). Otherwise, the quadtree leaf node willbe further partitioned by the binary tree. Therefore, the quadtree leafnode is also the root node for the binary tree and has the binary treedepth as 0. When the binary tree depth reaches MaxBTDepth (4, in thisexample), no further splitting is permitted. A binary tree node having awidth equal to MinBTSize (4, in this example) implies that no furthervertical splitting (that is, dividing of the width) is permitted forthat binary tree node. Similarly, a binary tree node having a heightequal to MinBTSize implies no further horizontal splitting (that is,dividing of the height) is permitted for that binary tree node. As notedabove, leaf nodes of the binary tree are referred to as CUs, and arefurther processed according to prediction and transform without furtherpartitioning.

FIG. 3 is a block diagram illustrating an example video encoder 200 thatmay perform the techniques of this disclosure. FIG. 3 is provided forpurposes of explanation and should not be considered limiting of thetechniques as broadly exemplified and described in this disclosure. Forpurposes of explanation, this disclosure describes video encoder 200according to the techniques of VVC (ITU-T H.266, under development), andHEVC (ITU-T H.265). However, the techniques of this disclosure may beperformed by video encoding devices that are configured to other videocoding standards.

In the example of FIG. 3, video encoder 200 includes video data memory230, mode selection unit 202, residual generation unit 204, transformprocessing unit 206, quantization unit 208, inverse quantization unit210, inverse transform processing unit 212, reconstruction unit 214,filter unit 216, decoded picture buffer (DPB) 218, and entropy encodingunit 220. Any or all of video data memory 230, mode selection unit 202,residual generation unit 204, transform processing unit 206,quantization unit 208, inverse quantization unit 210, inverse transformprocessing unit 212, reconstruction unit 214, filter unit 216, DPB 218,and entropy encoding unit 220 may be implemented in one or moreprocessors or in processing circuitry. For instance, the units of videoencoder 200 may be implemented as one or more circuits or logic elementsas part of hardware circuitry, or as part of a processor, ASIC, or FPGA.Moreover, video encoder 200 may include additional or alternativeprocessors or processing circuitry to perform these and other functions.

Video data memory 230 may store video data to be encoded by thecomponents of video encoder 200. Video encoder 200 may receive the videodata stored in video data memory 230 from, for example, video source 104(FIG. 1). DPB 218 may act as a reference picture memory that storesreference video data for use in prediction of subsequent video data byvideo encoder 200. Video data memory 230 and DPB 218 may be formed byany of a variety of memory devices, such as dynamic random access memory(DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. Video datamemory 230 and DPB 218 may be provided by the same memory device orseparate memory devices. In various examples, video data memory 230 maybe on-chip with other components of video encoder 200, as illustrated,or off-chip relative to those components.

In this disclosure, reference to video data memory 230 should not beinterpreted as being limited to memory internal to video encoder 200,unless specifically described as such, or memory external to videoencoder 200, unless specifically described as such. Rather, reference tovideo data memory 230 should be understood as reference memory thatstores video data that video encoder 200 receives for encoding (e.g.,video data for a current block that is to be encoded). Memory 106 ofFIG. 1 may also provide temporary storage of outputs from the variousunits of video encoder 200.

The various units of FIG. 3 are illustrated to assist with understandingthe operations performed by video encoder 200. The units may beimplemented as fixed-function circuits, programmable circuits, or acombination thereof. Fixed-function circuits refer to circuits thatprovide particular functionality, and are preset on the operations thatcan be performed. Programmable circuits refer to circuits that can beprogrammed to perform various tasks, and provide flexible functionalityin the operations that can be performed. For instance, programmablecircuits may execute software or firmware that cause the programmablecircuits to operate in the manner defined by instructions of thesoftware or firmware. Fixed-function circuits may execute softwareinstructions (e.g., to receive parameters or output parameters), but thetypes of operations that the fixed-function circuits perform aregenerally immutable. In some examples, one or more of the units may bedistinct circuit blocks (fixed-function or programmable), and in someexamples, one or more of the units may be integrated circuits.

Video encoder 200 may include arithmetic logic units (ALUs), elementaryfunction units (EFUs), digital circuits, analog circuits, and/orprogrammable cores, formed from programmable circuits. In examples wherethe operations of video encoder 200 are performed using softwareexecuted by the programmable circuits, memory 106 (FIG. 1) may store theinstructions (e.g., object code) of the software that video encoder 200receives and executes, or another memory within video encoder 200 (notshown) may store such instructions.

Video data memory 230 is configured to store received video data. Videoencoder 200 may retrieve a picture of the video data from video datamemory 230 and provide the video data to residual generation unit 204and mode selection unit 202. Video data in video data memory 230 may beraw video data that is to be encoded.

Mode selection unit 202 includes a motion estimation unit 222, a motioncompensation unit 224, and an intra-prediction unit 226. Mode selectionunit 202 may include additional functional units to perform videoprediction in accordance with other prediction modes. As examples, modeselection unit 202 may include a palette unit, an intra-block copy unit(which may be part of motion estimation unit 222 and/or motioncompensation unit 224), an affine unit, a linear model (LM) unit, or thelike.

Mode selection unit 202 generally coordinates multiple encoding passesto test combinations of encoding parameters and resultingrate-distortion values for such combinations. The encoding parametersmay include partitioning of CTUs into CUs, prediction modes for the CUs,transform types for residual data of the CUs, quantization parametersfor residual data of the CUs, and so on. Mode selection unit 202 mayultimately select the combination of encoding parameters havingrate-distortion values that are better than the other testedcombinations.

Video encoder 200 may partition a picture retrieved from video datamemory 230 into a series of CTUs, and encapsulate one or more CTUswithin a slice. Mode selection unit 202 may partition a CTU of thepicture in accordance with a tree structure, such as the QTBT structureor the quad-tree structure of HEVC described above. As described above,video encoder 200 may form one or more CUs from partitioning a CTUaccording to the tree structure. Such a CU may also be referred togenerally as a “video block” or “block.”

In general, mode selection unit 202 also controls the components thereof(e.g., motion estimation unit 222, motion compensation unit 224, andintra-prediction unit 226) to generate a prediction block for a currentblock (e.g., a current CU, or in HEVC, the overlapping portion of a PUand a TU). For inter-prediction of a current block, motion estimationunit 222 may perform a motion search to identify one or more closelymatching reference blocks in one or more reference pictures (e.g., oneor more previously coded pictures stored in DPB 218). In particular,motion estimation unit 222 may calculate a value representative of howsimilar a potential reference block is to the current block, e.g.,according to sum of absolute difference (SAD), sum of squareddifferences (SSD), mean absolute difference (MAD), mean squareddifferences (MSD), or the like. Motion estimation unit 222 may generallyperform these calculations using sample-by-sample differences betweenthe current block and the reference block being considered. Motionestimation unit 222 may identify a reference block having a lowest valueresulting from these calculations, indicating a reference block thatmost closely matches the current block.

Motion estimation unit 222 may form one or more motion vectors (MVs)that defines the positions of the reference blocks in the referencepictures relative to the position of the current block in a currentpicture. Motion estimation unit 222 may then provide the motion vectorsto motion compensation unit 224. For example, for uni-directionalinter-prediction, motion estimation unit 222 may provide a single motionvector, whereas for bi-directional inter-prediction, motion estimationunit 222 may provide two motion vectors. Motion compensation unit 224may then generate a prediction block using the motion vectors. Forexample, motion compensation unit 224 may retrieve data of the referenceblock using the motion vector. As another example, if the motion vectorhas fractional sample precision, motion compensation unit 224 mayinterpolate values for the prediction block according to one or moreinterpolation filters. Moreover, for bi-directional inter-prediction,motion compensation unit 224 may retrieve data for two reference blocksidentified by respective motion vectors and combine the retrieved data,e.g., through sample-by-sample averaging or weighted averaging.

As another example, for intra-prediction, or intra-prediction coding,intra-prediction unit 226 may generate the prediction block from samplesneighboring the current block. For example, for directional modes,intra-prediction unit 226 may generally mathematically combine values ofneighboring samples and populate these calculated values in the defineddirection across the current block to produce the prediction block. Asanother example, for DC mode, intra-prediction unit 226 may calculate anaverage of the neighboring samples to the current block and generate theprediction block to include this resulting average for each sample ofthe prediction block.

Mode selection unit 202 provides the prediction block to residualgeneration unit 204. Residual generation unit 204 receives a raw,unencoded version of the current block from video data memory 230 andthe prediction block from mode selection unit 202. Residual generationunit 204 calculates sample-by-sample differences between the currentblock and the prediction block. The resulting sample-by-sampledifferences define a residual block for the current block. In someexamples, residual generation unit 204 may also determine differencesbetween sample values in the residual block to generate a residual blockusing residual differential pulse code modulation (RDPCM). In someexamples, residual generation unit 204 may be formed using one or moresubtractor circuits that perform binary subtraction.

In examples where mode selection unit 202 partitions CUs into PUs, eachPU may be associated with a luma prediction unit and correspondingchroma prediction units. Video encoder 200 and video decoder 300 maysupport PUs having various sizes. As indicated above, the size of a CUmay refer to the size of the luma coding block of the CU and the size ofa PU may refer to the size of a luma prediction unit of the PU. Assumingthat the size of a particular CU is 2N×2N, video encoder 200 may supportPU sizes of 2N×2N or N×N for intra prediction, and symmetric PU sizes of2N×2N, 2N×N, N×2N, N×N, or similar for inter prediction. Video encoder200 and video decoder 300 may also support asymmetric partitioning forPU sizes of 2N×nU, 2N×nD, nL×2N, and nR×2N for inter prediction.

In examples where mode selection unit 202 does not further partition aCU into PUs, each CU may be associated with a luma coding block andcorresponding chroma coding blocks. As above, the size of a CU may referto the size of the luma coding block of the CU. The video encoder 200and video decoder 300 may support CU sizes of 2N×2N, 2N×N, or N×2N.

For other video coding techniques such as an intra-block copy modecoding, an affine-mode coding, and linear model (LM) mode coding, assome examples, mode selection unit 202, via respective units associatedwith the coding techniques, generates a prediction block for the currentblock being encoded. In some examples, such as palette mode coding, modeselection unit 202 may not generate a prediction block, and insteadgenerate syntax elements that indicate the manner in which toreconstruct the block based on a selected palette. In such modes, modeselection unit 202 may provide these syntax elements to entropy encodingunit 220 to be encoded.

As described above, residual generation unit 204 receives the video datafor the current block and the corresponding prediction block. Residualgeneration unit 204 then generates a residual block for the currentblock. To generate the residual block, residual generation unit 204calculates sample-by-sample differences between the prediction block andthe current block.

Transform processing unit 206 applies one or more transforms to theresidual block to generate a block of transform coefficients (referredto herein as a “transform coefficient block”). Transform processing unit206 may apply various transforms to a residual block to form thetransform coefficient block. For example, transform processing unit 206may apply a discrete cosine transform (DCT), a directional transform, aKarhunen-Loeve transform (KLT), or a conceptually similar transform to aresidual block. In some examples, transform processing unit 206 mayperform multiple transforms to a residual block, e.g., a primarytransform and a secondary transform, such as a rotational transform. Insome examples, transform processing unit 206 does not apply transformsto a residual block.

Quantization unit 208 may quantize the transform coefficients in atransform coefficient block, to produce a quantized transformcoefficient block. Quantization unit 208 may quantize transformcoefficients of a transform coefficient block according to aquantization parameter (QP) value associated with the current block.Video encoder 200 (e.g., via mode selection unit 202) may adjust thedegree of quantization applied to the transform coefficient blocksassociated with the current block by adjusting the QP value associatedwith the CU. Quantization may introduce loss of information, and thus,quantized transform coefficients may have lower precision than theoriginal transform coefficients produced by transform processing unit206.

Inverse quantization unit 210 and inverse transform processing unit 212may apply inverse quantization and inverse transforms to a quantizedtransform coefficient block, respectively, to reconstruct a residualblock from the transform coefficient block. Reconstruction unit 214 mayproduce a reconstructed block corresponding to the current block (albeitpotentially with some degree of distortion) based on the reconstructedresidual block and a prediction block generated by mode selection unit202. For example, reconstruction unit 214 may add samples of thereconstructed residual block to corresponding samples from theprediction block generated by mode selection unit 202 to produce thereconstructed block.

Filter unit 216 may perform one or more filter operations onreconstructed blocks. For example, filter unit 216 may performdeblocking operations to reduce blockiness artifacts along edges of CUs.Operations of filter unit 216 may be skipped, in some examples.

Video encoder 200 stores reconstructed blocks in DPB 218. For instance,in examples where operations of filter unit 216 are not performed,reconstruction unit 214 may store reconstructed blocks to DPB 218. Inexamples where operations of filter unit 216 are performed, filter unit216 may store the filtered reconstructed blocks to DPB 218. Motionestimation unit 222 and motion compensation unit 224 may retrieve areference picture from DPB 218, formed from the reconstructed (andpotentially filtered) blocks, to inter-predict blocks of subsequentlyencoded pictures. In addition, intra-prediction unit 226 may usereconstructed blocks in DPB 218 of a current picture to intra-predictother blocks in the current picture.

In general, entropy encoding unit 220 may entropy encode syntax elementsreceived from other functional components of video encoder 200. Forexample, entropy encoding unit 220 may entropy encode quantizedtransform coefficient blocks from quantization unit 208. As anotherexample, entropy encoding unit 220 may entropy encode prediction syntaxelements (e.g., motion information for inter-prediction or intra-modeinformation for intra-prediction) from mode selection unit 202. Entropyencoding unit 220 may perform one or more entropy encoding operations onthe syntax elements, which are another example of video data, togenerate entropy-encoded data. For example, entropy encoding unit 220may perform a context-adaptive variable length coding (CAVLC) operation,a CABAC operation, a variable-to-variable (V2V) length coding operation,a syntax-based context-adaptive binary arithmetic coding (SBAC)operation, a Probability Interval Partitioning Entropy (PIPE) codingoperation, an Exponential-Golomb encoding operation, or another type ofentropy encoding operation on the data. In some examples, entropyencoding unit 220 may operate in bypass mode where syntax elements arenot entropy encoded.

Video encoder 200 may output a bitstream that includes the entropyencoded syntax elements needed to reconstruct blocks of a slice orpicture. In particular, entropy encoding unit 220 may output thebitstream.

The operations described above are described with respect to a block.Such description should be understood as being operations for a lumacoding block and/or chroma coding blocks. As described above, in someexamples, the luma coding block and chroma coding blocks are luma andchroma components of a CU. In some examples, the luma coding block andthe chroma coding blocks are luma and chroma components of a PU.

In some examples, operations performed with respect to a luma codingblock need not be repeated for the chroma coding blocks. As one example,operations to identify a motion vector (MV) and reference picture for aluma coding block need not be repeated for identifying a MV andreference picture for the chroma blocks. Rather, the MV for the lumacoding block may be scaled to determine the MV for the chroma blocks,and the reference picture may be the same. As another example, theintra-prediction process may be the same for the luma coding block andthe chroma coding blocks.

Video encoder 200 represents an example of a device configured to encodevideo data including a memory configured to store video data, and one ormore processing units implemented in circuitry and configured to derive,for a current block of video data and using decoder side intra modederivation (DIMD), a list of intra modes using reconstructed samples ofneighboring blocks; construct, for the current block, a most possiblemode (MPM) list that includes at least one intra mode from the derivedlist of intra modes; and predict, using a candidate selected from theconstructed MPM list, the current block.

FIG. 4 is a block diagram illustrating an example video decoder 300 thatmay perform the techniques of this disclosure. FIG. 4 is provided forpurposes of explanation and is not limiting on the techniques as broadlyexemplified and described in this disclosure. For purposes ofexplanation, this disclosure describes video decoder 300 according tothe techniques of VVC (ITU-T H.266, under development), and HEVC (ITU-TH.265). However, the techniques of this disclosure may be performed byvideo coding devices that are configured to other video codingstandards.

In the example of FIG. 4, video decoder 300 includes coded picturebuffer (CPB) memory 320, entropy decoding unit 302, predictionprocessing unit 304, inverse quantization unit 306, inverse transformprocessing unit 308, reconstruction unit 310, filter unit 312, anddecoded picture buffer (DPB) 314. Any or all of CPB memory 320, entropydecoding unit 302, prediction processing unit 304, inverse quantizationunit 306, inverse transform processing unit 308, reconstruction unit310, filter unit 312, and DPB 314 may be implemented in one or moreprocessors or in processing circuitry. For instance, the units of videodecoder 300 may be implemented as one or more circuits or logic elementsas part of hardware circuitry, or as part of a processor, ASIC, or FPGA.Moreover, video decoder 300 may include additional or alternativeprocessors or processing circuitry to perform these and other functions.

Prediction processing unit 304 includes motion compensation unit 316 andintra-prediction unit 318. Prediction processing unit 304 may includeadditional units to perform prediction in accordance with otherprediction modes. As examples, prediction processing unit 304 mayinclude a palette unit, an intra-block copy unit (which may form part ofmotion compensation unit 316), an affine unit, a linear model (LM) unit,or the like. In other examples, video decoder 300 may include more,fewer, or different functional components.

CPB memory 320 may store video data, such as an encoded video bitstream,to be decoded by the components of video decoder 300. The video datastored in CPB memory 320 may be obtained, for example, fromcomputer-readable medium 110 (FIG. 1). CPB memory 320 may include a CPBthat stores encoded video data (e.g., syntax elements) from an encodedvideo bitstream. Also, CPB memory 320 may store video data other thansyntax elements of a coded picture, such as temporary data representingoutputs from the various units of video decoder 300. DPB 314 generallystores decoded pictures, which video decoder 300 may output and/or useas reference video data when decoding subsequent data or pictures of theencoded video bitstream. CPB memory 320 and DPB 314 may be formed by anyof a variety of memory devices, such as DRAM, including SDRAM, MRAM,RRAM, or other types of memory devices. CPB memory 320 and DPB 314 maybe provided by the same memory device or separate memory devices. Invarious examples, CPB memory 320 may be on-chip with other components ofvideo decoder 300, or off-chip relative to those components.

Additionally or alternatively, in some examples, video decoder 300 mayretrieve coded video data from memory 120 (FIG. 1). That is, memory 120may store data as discussed above with CPB memory 320. Likewise, memory120 may store instructions to be executed by video decoder 300, whensome or all of the functionality of video decoder 300 is implemented insoftware to be executed by processing circuitry of video decoder 300.

The various units shown in FIG. 4 are illustrated to assist withunderstanding the operations performed by video decoder 300. The unitsmay be implemented as fixed-function circuits, programmable circuits, ora combination thereof. Similar to FIG. 3, fixed-function circuits referto circuits that provide particular functionality, and are preset on theoperations that can be performed. Programmable circuits refer tocircuits that can be programmed to perform various tasks, and provideflexible functionality in the operations that can be performed. Forinstance, programmable circuits may execute software or firmware thatcause the programmable circuits to operate in the manner defined byinstructions of the software or firmware. Fixed-function circuits mayexecute software instructions (e.g., to receive parameters or outputparameters), but the types of operations that the fixed-functioncircuits perform are generally immutable. In some examples, one or moreof the units may be distinct circuit blocks (fixed-function orprogrammable), and in some examples, one or more of the units may beintegrated circuits.

Video decoder 300 may include ALUs, EFUs, digital circuits, analogcircuits, and/or programmable cores formed from programmable circuits.In examples where the operations of video decoder 300 are performed bysoftware executing on the programmable circuits, on-chip or off-chipmemory may store instructions (e.g., object code) of the software thatvideo decoder 300 receives and executes.

Entropy decoding unit 302 may receive encoded video data from the CPBand entropy decode the video data to reproduce syntax elements.Prediction processing unit 304, inverse quantization unit 306, inversetransform processing unit 308, reconstruction unit 310, and filter unit312 may generate decoded video data based on the syntax elementsextracted from the bitstream.

In general, video decoder 300 reconstructs a picture on a block-by-blockbasis. Video decoder 300 may perform a reconstruction operation on eachblock individually (where the block currently being reconstructed, i.e.,decoded, may be referred to as a “current block”).

Entropy decoding unit 302 may entropy decode syntax elements definingquantized transform coefficients of a quantized transform coefficientblock, as well as transform information, such as a quantizationparameter (QP) and/or transform mode indication(s). Inverse quantizationunit 306 may use the QP associated with the quantized transformcoefficient block to determine a degree of quantization and, likewise, adegree of inverse quantization for inverse quantization unit 306 toapply. Inverse quantization unit 306 may, for example, perform a bitwiseleft-shift operation to inverse quantize the quantized transformcoefficients. Inverse quantization unit 306 may thereby form a transformcoefficient block including transform coefficients.

After inverse quantization unit 306 forms the transform coefficientblock, inverse transform processing unit 308 may apply one or moreinverse transforms to the transform coefficient block to generate aresidual block associated with the current block. For example, inversetransform processing unit 308 may apply an inverse DCT, an inverseinteger transform, an inverse Karhunen-Loeve transform (KLT), an inverserotational transform, an inverse directional transform, or anotherinverse transform to the transform coefficient block.

Furthermore, prediction processing unit 304 generates a prediction blockaccording to prediction information syntax elements that were entropydecoded by entropy decoding unit 302. For example, if the predictioninformation syntax elements indicate that the current block isinter-predicted, motion compensation unit 316 may generate theprediction block. In this case, the prediction information syntaxelements may indicate a reference picture in DPB 314 from which toretrieve a reference block, as well as a motion vector identifying alocation of the reference block in the reference picture relative to thelocation of the current block in the current picture. Motioncompensation unit 316 may generally perform the inter-prediction processin a manner that is substantially similar to that described with respectto motion compensation unit 224 (FIG. 3).

As another example, if the prediction information syntax elementsindicate that the current block is intra-predicted, intra-predictionunit 318 may generate the prediction block according to anintra-prediction mode indicated by the prediction information syntaxelements. Again, intra-prediction unit 318 may generally perform theintra-prediction process in a manner that is substantially similar tothat described with respect to intra-prediction unit 226 (FIG. 3).Intra-prediction unit 318 may retrieve data of neighboring samples tothe current block from DPB 314.

Reconstruction unit 310 may reconstruct the current block using theprediction block and the residual block. For example, reconstructionunit 310 may add samples of the residual block to corresponding samplesof the prediction block to reconstruct the current block.

Filter unit 312 may perform one or more filter operations onreconstructed blocks. For example, filter unit 312 may performdeblocking operations to reduce blockiness artifacts along edges of thereconstructed blocks. Operations of filter unit 312 are not necessarilyperformed in all examples.

Video decoder 300 may store the reconstructed blocks in DPB 314. Forinstance, in examples where operations of filter unit 312 are notperformed, reconstruction unit 310 may store reconstructed blocks to DPB314. In examples where operations of filter unit 312 are performed,filter unit 312 may store the filtered reconstructed blocks to DPB 314.As discussed above, DPB 314 may provide reference information, such assamples of a current picture for intra-prediction and previously decodedpictures for subsequent motion compensation, to prediction processingunit 304. Moreover, video decoder 300 may output decoded pictures (e.g.,decoded video) from DPB 314 for subsequent presentation on a displaydevice, such as display device 118 of FIG. 1.

In this manner, video decoder 300 represents an example of a videodecoding device including a memory configured to store video data, andone or more processing units implemented in circuitry and configured toderive, for a current block of video data and using decoder side intramode derivation (DIMD), a list of intra modes using reconstructedsamples of neighboring blocks; construct, for the current block, a mostpossible mode (MPM) list that includes at least one intra mode from thederived list of intra modes; and predict, using a candidate selectedfrom the constructed MPM list, the current block.

FIG. 15 is a flowchart illustrating an example method for encoding acurrent block in accordance with the techniques of this disclosure. Thecurrent block may comprise a current CU. Although described with respectto video encoder 200 (FIGS. 1 and 3), it should be understood that otherdevices may be configured to perform a method similar to that of FIG.15.

In this example, video encoder 200 initially predicts the current block(350). For example, video encoder 200 may form a prediction block forthe current block. Video encoder 200 may then calculate a residual blockfor the current block (352). To calculate the residual block, videoencoder 200 may calculate a difference between the original, unencodedblock and the prediction block for the current block. Video encoder 200may then transform the residual block and quantize transformcoefficients of the residual block (354). Next, video encoder 200 mayscan the quantized transform coefficients of the residual block (356).During the scan, or following the scan, video encoder 200 may entropyencode the transform coefficients (358). For example, video encoder 200may encode the transform coefficients using CAVLC or CABAC. Videoencoder 200 may then output the entropy encoded data of the block (360).

FIG. 16 is a flowchart illustrating an example method for decoding acurrent block of video data in accordance with the techniques of thisdisclosure. The current block may comprise a current CU. Althoughdescribed with respect to video decoder 300 (FIGS. 1 and 4), it shouldbe understood that other devices may be configured to perform a methodsimilar to that of FIG. 16.

Video decoder 300 may receive entropy encoded data for the currentblock, such as entropy encoded prediction information and entropyencoded data for transform coefficients of a residual blockcorresponding to the current block (370). Video decoder 300 may entropydecode the entropy encoded data to determine prediction information forthe current block and to reproduce transform coefficients of theresidual block (372). Video decoder 300 may predict the current block(374), e.g., using an intra- or inter-prediction mode as indicated bythe prediction information for the current block, to calculate aprediction block for the current block. Video decoder 300 may theninverse scan the reproduced transform coefficients (376), to create ablock of quantized transform coefficients. Video decoder 300 may theninverse quantize the transform coefficients and apply an inversetransform to the transform coefficients to produce a residual block(378). Video decoder 300 may ultimately decode the current block bycombining the prediction block and the residual block (380).

FIG. 17 is a flowchart illustrating an example technique for encodingvideo data using DIMD, in accordance with one or more techniques of thisdisclosure. Although described with respect to video encoder 200 (FIGS.1 and 3), it should be understood that other devices may be configuredto perform a method similar to that of FIG. 17.

Video encoder 200 may derive, for a current block of video data, a listof decoder side intra mode derivation (DIMD) intra modes usingreconstructed samples of neighboring blocks (1702). For instance,intra-prediction unit 226 may derive the DIMD intra modes using thetechnique discussed above with reference to FIG. 7 to obtain a firstDIMD intra mode M1 and a second DIMD intra mode M2.

Video encoder 200 may construct, for the current block, a most probablemode (MPM) list that includes at least one intra mode from the DIMDmodes (1704). For instance, intra-prediction unit 226 may construct theMPM list using the technique discussed above with reference to FIG. 11.The constructed MPM list may include one or both of the first DIMD intramode M1 and the second DIMD intra mode M2.

Video encoder 200 may determine whether to predict the current blockusing DIMD (1706). For instance, mode selection unit 202 may performanalysis to determine an optimal encoding mode for the current block(e.g., a coding mode that uses the fewest bits to represent the currentblock). To determine the optimal encoding mode, mode selection unit 202may test encoding the current block using various modes. Where modeselection unit 202 determines that encoding the current block using DIMDis optimal, mode selection unit 202 may determine to encode the currentblock using DIMD. Similarly, where mode selection unit 202 determinesthat encoding the current block using one of the derived DIMD modes inthe MPM list, mode selection unit 202 may determine not the encode thecurrent block using DIMD.

Video encoder 200 may encode an indication of whether the current blockis predicted using DIMD. For instance, entropy encoding unit 220 mayencode, for the current block, a DIMD flag having a value that indicateswhether DIMD is enabled for the current block of video data. As oneexample, responsive to determining not to predict the current blockusing DIMD (“No” branch of 1706), video encoder 200 may encode the DIMDflag with a false (e.g., 0) value to indicate that the current block isnot predicted using DIMD (1708). As another example, responsive todetermining to predict the current block using DIMD (“Yes” branch of1706), video encoder 200 may encode the DIMD flag with a true (e.g., 1)value to indicate that the current block is predicted using DIMD (1714).

Video encoder 200 may encode one or more syntax elements indicating aselected intra mode from the MPM list (1710). For instance, entropyencoding unit 220 may encode a syntax element having a value thatindicates an index in the MPM list of the selected intra mode.

In some examples, as discussed above, video encoder 200 may include areconstruction loop in which blocks of video data a reconstructed to beused as reference when predicting subsequent blocks. As one example,where the current block is not predicted using DIMD, video encoder 200may predict the current block using the selected intra mode (1712). Forinstance, intra-prediction unit 226 may generate a prediction blockusing samples in the direction specified by the selected intra mode. Asanother example, where the current block is predicted using DIMD, videoencoder 200 may predict the current block using DIMD (1716). Forinstance, intra-prediction unit 226 may predict the current block usingthe technique described above with reference to FIG. 8.

FIG. 18 is a flowchart illustrating an example technique for decodingvideo data using DIMD, in accordance with one or more techniques of thisdisclosure. Although described with respect to video decoder 300 (FIGS.1 and 4), it should be understood that other devices may be configuredto perform a method similar to that of FIG. 18.

Video decoder 300 may derive, for a current block of video data, a listof decoder side intra mode derivation (DIMD) intra modes usingreconstructed samples of neighboring blocks (1802). For instance,intra-prediction unit 318 may derive the DIMD intra modes using thetechnique discussed above with reference to FIG. 7 to obtain a firstDIMD intra mode M1 and a second DIMD intra mode M2.

Video decoder 300 may construct, for the current block, a most probablemode (MPM) list that includes at least one intra mode from the DIMDmodes (1804). For instance, intra-prediction unit 318 may construct theMPM list using the technique discussed above with reference to FIG. 11.The constructed MPM list may include one or both of the first DIMD intramode M1 and the second DIMD intra mode M2.

Video decoder 300 may determine whether to predict the current blockusing DIMD (1806). For instance, entropy decoding unit 302 may decode,for the current block, a DIMD flag having a value that indicates whetherDIMD is enabled for the current block of video data. Based on the valueof the DIMD flag, intra-prediction unit 318 may determine whether topredict the current block using DIMD. As one example, where the value ofthe flag is true (e.g., 1), intra-prediction unit 318 may determine topredict the current block using DIMD. As another example, where thevalue of the flag is false (e.g., 0), intra-prediction unit 318 maydetermine not to predict the current block using DIMD. As noted above,in some examples, video decoder 300 may derive the list of DIMD intramodes regardless of the value of the DIMD flag.

Where video decoder 300 determines to not predict the current blockusing DIMD (“No” branch of 1806), entropy decoding unit 302 may decodeone or more syntax elements indicating a selected intra mode from theMPM list (1808) (e.g., indicating an index in the MPM list). Forexample, entropy decoding unit 302 may decode a intra_luma_mpm_idxsyntax element that specifies the index in the MPM list of the selectedintra mode.

Video decoder 300 may predict, using the candidate selected from theconstructed MPM list, the current block (1810). For instance,intra-prediction unit 318 may generate a prediction block for thecurrent block using the selected intra mode from the MPM list.Reconstruction unit 310 may combine the prediction block with a residualblock (e.g., similar to 380 of FIG. 16).

Where video decoder 300 determines to predict the current block usingDIMD (“Yes” branch of 1806), entropy decoding unit 302 may predict thecurrent block using DIMD (1812). For instance, intra-prediction unit 318may predict the current block using the technique described above withreference to FIG. 8.

The following numbered clauses may illustrate one or more examples ofthis disclosure:

Clause 1A. A method of decoding video data, the method comprising:deriving, for a current block of video data and using decoder side intramode derivation (DIMD), a list of intra modes using reconstructedsamples of neighboring blocks; constructing, for the current block, amost possible mode (MPM) list that includes at least one intra mode fromthe derived list of intra modes; and predicting, using a candidateselected from the constructed MPM list, the current block.

Clause 2A. The method of clause 1A, wherein deriving the list of intramodes using DIMD comprises deriving the list of intra modes using DIMDregardless of a value of a DIMD flag.

Clause 3A. The method of clause 1A or clause 2A, wherein constructingthe MPM list comprises: inserting, into the MPM list, a first candidatefrom the list of intra modes derived using DIMD; and selectivelyinserting, based on a sum of intensity of a second candidate from thelist of intra modes derived using DIMD, the second candidate into theMPM list.

Clause 4A. The method of clause 3A, wherein constructing the MPM listfurther comprises: inserting, into the MPM list and after the firstcandidate, additional intra mode candidates.

Clause 5A. A device for coding video data, the device comprising one ormore means for performing the method of any of clauses 1A-4A.

Clause 6A. The device of clause 5A, wherein the one or more meanscomprise one or more processors implemented in circuitry.

Clause 7A. The device of any of clauses 5A and 6A, further comprising amemory to store the video data.

Clause 8A. The device of any of clauses 5A-7A, further comprising adisplay configured to display decoded video data.

Clause 9A. The device of any of clauses 5A-8A, wherein the devicecomprises one or more of a camera, a computer, a mobile device, abroadcast receiver device, or a set-top box.

Clause 10A. A computer-readable storage medium having stored thereoninstructions that, when executed, cause one or more processors toperform the method of any of clauses 1A-4A.

Clause 1B. A method of decoding video data, the method comprising:deriving, for a current block of video data and using decoder side intramode derivation (DIMD), a list of intra modes using reconstructedsamples of neighboring blocks; constructing, for the current block, amost probable mode (MPM) list, wherein constructing the MPM listcomprises inserting, into the MPM list, at least one intra mode from thederived list of intra modes; and predicting, using a candidate selectedfrom the constructed MPM list, the current block.

Clause 2B. The method of clause 1B, further comprising: decoding, forthe current block, a DIMD flag having a value that indicates whetherDIMD is enabled for the current block of video data, wherein derivingthe list of intra modes using DIMD comprises deriving the list of intramodes using DIMD regardless of a value of the DIMD flag.

Clause 3B. The method of clause 1B, wherein inserting the at least oneintra mode from the derived list of intra modes into the MPM listcomprises: inserting, into the MPM list, a first candidate from the listof intra modes derived using DIMD; and selectively inserting, in to theMPM list, a second candidate from the list of intra modes derived usingDIMD.

Clause 4B. The method of clause 3B, wherein selectively inserting thesecond candidate comprises selectively inserting, based on a sum ofintensity of the second candidate from the list of intra modes derivedusing DIMD, the second candidate into the MPM list.

Clause 5B. The method of clause 1B, wherein constructing the MPM listfurther comprises: inserting, into the MPM list and after the at leastone intra mode from the derived list of intra modes, additional intramode candidates.

Clause 6B. The method of clause 5B, wherein inserting the additionalintra mode candidates comprises: inserting, into the MPM list and afterthe at least one intra mode from the derived list of intra modes, one ormore default candidates.

Clause 7B. The method of clause 5B, wherein constructing the MPM listfurther comprises: inserting, into the MPM list and before the at leastone intra mode from the derived list of intra modes, one or more intramode candidates that are prediction modes from neighboring blocks of thecurrent block.

Clause 8B. A method of encoding video data, the method comprising:deriving, for a current block of video data and using decoder side intramode derivation (DIMD), a list of intra modes using reconstructedsamples of neighboring blocks; constructing, for the current block, amost probable mode (MPM) list, wherein constructing the MPM listcomprises inserting, into the MPM list, at least one intra mode from thederived list of intra modes; selecting, for the current block and fromthe MPM list, a candidate intra mode; and encoding, for the currentblock, one or more syntax element that specify the candidate intra mode.

Clause 9B. The method of clause 8B, further comprising: encoding, forthe current block, a DIMD flag having a value that indicates whetherDIMD is enabled for the current block of video data, wherein derivingthe list of intra modes using DIMD comprises deriving the list of intramodes using DIMD regardless of a value of the DIMD flag.

Clause 10B. The method of clause 8B, wherein inserting the at least oneintra mode from the derived list of intra modes into the MPM listcomprises: inserting, into the MPM list, a first candidate from the listof intra modes derived using DIMD; and selectively inserting, in to theMPM list, a second candidate from the list of intra modes derived usingDIMD.

Clause 11B. The method of clause 10B, wherein selectively inserting thesecond candidate comprises selectively inserting, based on a sum ofintensity of the second candidate from the list of intra modes derivedusing DIMD, the second candidate into the MPM list.

Clause 12B. The method of clause 8B, wherein constructing the MPM listfurther comprises: inserting, into the MPM list and after the at leastone intra mode from the derived list of intra modes, additional intramode candidates.

Clause 13B. The method of clause 12B, wherein inserting the additionalintra mode candidates comprises: inserting, into the MPM list and afterthe at least one intra mode from the derived list of intra modes, one ormore default candidates.

Clause 14B. The method of clause 12B, wherein constructing the MPM listfurther comprises: inserting, into the MPM list and before the at leastone intra mode from the derived list of intra modes, one or more intramode candidates that are prediction modes from neighboring blocks of thecurrent block.

Clause 15B. A device for decoding video data, the device comprising: amemory configured to store video data; and one or more processorsimplemented in circuitry and configured to: derive, for a current blockof video data and using decoder side intra mode derivation (DIMD), alist of intra modes using reconstructed samples of neighboring blocks;construct, for the current block, a most probable mode (MPM) list,wherein constructing the MPM list comprises inserting, into the MPMlist, at least one intra mode from the derived list of intra modes; andpredict, using a candidate selected from the constructed MPM list, thecurrent block.

Clause 16B. The device of clause 15B, wherein the one or more processorsare further configured to: decode, for the current block, a DIMD flaghaving a value that indicates whether DIMD is enabled for the currentblock of video data, wherein, to derive the list of intra modes usingDIMD, the one or more processors are configured to derive the list ofintra modes using DIMD regardless of a value of the DIMD flag.

Clause 17B. The device of clause 15B, wherein, to insert the at leastone intra mode from the derived list of intra modes into the MPM list,the one or more processors are configured to: insert, into the MPM list,a first candidate from the list of intra modes derived using DIMD; andselectively insert, in to the MPM list, a second candidate from the listof intra modes derived using DIMD.

Clause 18B. The device of clause 17B, wherein, to selectively insert thesecond candidate, the one or more processors are configured toselectively insert, based on a sum of intensity of the second candidatefrom the list of intra modes derived using DIMD, the second candidateinto the MPM list.

Clause 19B. The device of clause 15B, wherein, to construct the MPMlist, the one or more processors are configured to: insert, into the MPMlist and after the at least one intra mode from the derived list ofintra modes, additional intra mode candidates.

Clause 20B. The device of clause 19B, wherein, to insert the additionalintra mode candidates, the one or more processors are configured to:insert, into the MPM list and after the at least one intra mode from thederived list of intra modes, one or more default candidates.

Clause 21B. The device of clause 19B, wherein, to construct the MPMlist, the one or more processors are configured to: insert, into the MPMlist and before the at least one intra mode from the derived list ofintra modes, one or more intra mode candidates that are prediction modesfrom neighboring blocks of the current block.

Clause 22B. A device for encoding video data, the device comprising: amemory configured to store video data; and one or more processorsimplemented in circuitry and configured to: derive, for a current blockof video data and using decoder side intra mode derivation (DIMD), alist of intra modes using reconstructed samples of neighboring blocks;construct, for the current block, a most probable mode (MPM) list,wherein constructing the MPM list comprises inserting, into the MPMlist, at least one intra mode from the derived list of intra modes;select, for the current block and from the MPM list, a candidate intramode; and encode, for the current block, one or more syntax element thatspecify the candidate intra mode.

Clause 23B. The device of clause 22B, wherein the one or more processorsare further configured to: encode, for the current block, a DIMD flaghaving a value that indicates whether DIMD is enabled for the currentblock of video data, wherein, to derive the list of intra modes usingDIMD, the one or more processors are configured to derive the list ofintra modes using DIMD regardless of a value of the DIMD flag.

Clause 24B. The device of clause 22B, wherein, to insert the at leastone intra mode from the derived list of intra modes into the MPM list,the one or more processors are configured to: insert, into the MPM list,a first candidate from the list of intra modes derived using DIMD; andselectively insert, in to the MPM list, a second candidate from the listof intra modes derived using DIMD.

Clause 25B. The device of clause 24B, wherein, to selectively insert thesecond candidate, the one or more processors are configured toselectively insert, based on a sum of intensity of the second candidatefrom the list of intra modes derived using DIMD, the second candidateinto the MPM list.

Clause 26B. The device of clause 22B, wherein, to construct the MPMlist, the one or more processors are configured to: insert, into the MPMlist and after the at least one intra mode from the derived list ofintra modes, additional intra mode candidates.

Clause 27B. The device of clause 26B, wherein, to insert the additionalintra mode candidates, the one or more processors are configured to:insert, into the MPM list and after the at least one intra mode from thederived list of intra modes, one or more default candidates.

Clause 28B. The device of clause 26B, wherein, to construct the MPMlist, the one or more processors are configured to: insert, into the MPMlist and before the at least one intra mode from the derived list ofintra modes, one or more intra mode candidates that are prediction modesfrom neighboring blocks of the current block.

Clause 1C. A method of decoding video data, the method comprising:deriving, for a current block of video data and using decoder side intramode derivation (DIMD), a list of intra modes using reconstructedsamples of neighboring blocks; constructing, for the current block, amost probable mode (MPM) list, wherein constructing the MPM listcomprises inserting, into the MPM list, at least one intra mode from thederived list of intra modes; and predicting, using a candidate selectedfrom the constructed MPM list, the current block.

Clause 2C. The method of clause 1C, further comprising: decoding, forthe current block, a DIMD flag having a value that indicates whetherDIMD is enabled for the current block of video data, wherein derivingthe list of intra modes using DIMD comprises deriving the list of intramodes using DIMD regardless of a value of the DIMD flag.

Clause 3C. The method of clause 1C or 2C, wherein inserting the at leastone intra mode from the derived list of intra modes into the MPM listcomprises: inserting, into the MPM list, a first candidate from the listof intra modes derived using DIMD; and selectively inserting, in to theMPM list, a second candidate from the list of intra modes derived usingDIMD.

Clause 4C. The method of clause 3C, wherein selectively inserting thesecond candidate comprises selectively inserting, based on a sum ofintensity of the second candidate from the list of intra modes derivedusing DIMD, the second candidate into the MPM list.

Clause 5C. The method of any of clauses 1C-4C, wherein constructing theMPM list further comprises: inserting, into the MPM list and after theat least one intra mode from the derived list of intra modes, additionalintra mode candidates.

Clause 6C. The method of clause 5C, wherein inserting the additionalintra mode candidates comprises: inserting, into the MPM list and afterthe at least one intra mode from the derived list of intra modes, one ormore default candidates.

Clause 7C. The method of clause 5C or 6C, wherein constructing the MPMlist further comprises: inserting, into the MPM list and before the atleast one intra mode from the derived list of intra modes, one or moreintra mode candidates that are prediction modes from neighboring blocksof the current block.

Clause 8C. A method of encoding video data, the method comprising:deriving, for a current block of video data and using decoder side intramode derivation (DIMD), a list of intra modes using reconstructedsamples of neighboring blocks; constructing, for the current block, amost probable mode (MPM) list, wherein constructing the MPM listcomprises inserting, into the MPM list, at least one intra mode from thederived list of intra modes; selecting, for the current block and fromthe MPM list, a candidate intra mode; and encoding, for the currentblock, one or more syntax element that specify the candidate intra mode.

Clause 9C. The method of clause 8C, further comprising: encoding, forthe current block, a DIMD flag having a value that indicates whetherDIMD is enabled for the current block of video data, wherein derivingthe list of intra modes using DIMD comprises deriving the list of intramodes using DIMD regardless of a value of the DIMD flag.

Clause 10C. The method of clause 8C or 9C, wherein inserting the atleast one intra mode from the derived list of intra modes into the MPMlist comprises: inserting, into the MPM list, a first candidate from thelist of intra modes derived using DIMD; and selectively inserting, in tothe MPM list, a second candidate from the list of intra modes derivedusing DIMD.

Clause 11C. The method of clause 10C, wherein selectively inserting thesecond candidate comprises selectively inserting, based on a sum ofintensity of the second candidate from the list of intra modes derivedusing DIMD, the second candidate into the MPM list.

Clause 12C. The method of any of clauses 8C-11C, wherein constructingthe MPM list further comprises: inserting, into the MPM list and afterthe at least one intra mode from the derived list of intra modes,additional intra mode candidates.

Clause 13C. The method of clause 12C, wherein inserting the additionalintra mode candidates comprises: inserting, into the MPM list and afterthe at least one intra mode from the derived list of intra modes, one ormore default candidates.

Clause 14C. The method of clause 12C or 13C, wherein constructing theMPM list further comprises: inserting, into the MPM list and before theat least one intra mode from the derived list of intra modes, one ormore intra mode candidates that are prediction modes from neighboringblocks of the current block.

Clause 15C. A device for decoding video data, the device comprising: amemory configured to store video data; and one or more processorsimplemented in circuitry and configured to: derive, for a current blockof video data and using decoder side intra mode derivation (DIMD), alist of intra modes using reconstructed samples of neighboring blocks;construct, for the current block, a most probable mode (MPM) list,wherein constructing the MPM list comprises inserting, into the MPMlist, at least one intra mode from the derived list of intra modes; andpredict, using a candidate selected from the constructed MPM list, thecurrent block.

Clause 16C. The device of clause 15C, wherein the one or more processorsare further configured to: decode, for the current block, a DIMD flaghaving a value that indicates whether DIMD is enabled for the currentblock of video data, wherein, to derive the list of intra modes usingDIMD, the one or more processors are configured to derive the list ofintra modes using DIMD regardless of a value of the DIMD flag.

Clause 17C. The device of clause 15C or 16C, wherein, to insert the atleast one intra mode from the derived list of intra modes into the MPMlist, the one or more processors are configured to: insert, into the MPMlist, a first candidate from the list of intra modes derived using DIMD;and selectively insert, in to the MPM list, a second candidate from thelist of intra modes derived using DIMD.

Clause 18C. The device of clause 17C, wherein, to selectively insert thesecond candidate, the one or more processors are configured toselectively insert, based on a sum of intensity of the second candidatefrom the list of intra modes derived using DIMD, the second candidateinto the MPM list.

Clause 19C. The device of any of clauses 15C-18C, wherein, to constructthe MPM list, the one or more processors are configured to: insert, intothe MPM list and after the at least one intra mode from the derived listof intra modes, additional intra mode candidates.

Clause 20C. The device of clause 19C, wherein, to insert the additionalintra mode candidates, the one or more processors are configured to:insert, into the MPM list and after the at least one intra mode from thederived list of intra modes, one or more default candidates.

Clause 21C. The device of clause 19C or 20C, wherein, to construct theMPM list, the one or more processors are configured to: insert, into theMPM list and before the at least one intra mode from the derived list ofintra modes, one or more intra mode candidates that are prediction modesfrom neighboring blocks of the current block.

Clause 22C. A device for encoding video data, the device comprising: amemory configured to store video data; and one or more processorsimplemented in circuitry and configured to: derive, for a current blockof video data and using decoder side intra mode derivation (DIMD), alist of intra modes using reconstructed samples of neighboring blocks;construct, for the current block, a most probable mode (MPM) list,wherein constructing the MPM list comprises inserting, into the MPMlist, at least one intra mode from the derived list of intra modes;select, for the current block and from the MPM list, a candidate intramode; and encode, for the current block, one or more syntax element thatspecify the candidate intra mode.

Clause 23C. The device of clause 22C, wherein the one or more processorsare further configured to: encode, for the current block, a DIMD flaghaving a value that indicates whether DIMD is enabled for the currentblock of video data, wherein, to derive the list of intra modes usingDIMD, the one or more processors are configured to derive the list ofintra modes using DIMD regardless of a value of the DIMD flag.

Clause 24C. The device of clause 22C or 23C, wherein, to insert the atleast one intra mode from the derived list of intra modes into the MPMlist, the one or more processors are configured to: insert, into the MPMlist, a first candidate from the list of intra modes derived using DIMD;and selectively insert, in to the MPM list, a second candidate from thelist of intra modes derived using DIMD.

Clause 25C. The device of clause 24C, wherein, to selectively insert thesecond candidate, the one or more processors are configured toselectively insert, based on a sum of intensity of the second candidatefrom the list of intra modes derived using DIMD, the second candidateinto the MPM list.

Clause 26C. The device of any of clauses 22C-25C, wherein, to constructthe MPM list, the one or more processors are configured to: insert, intothe MPM list and after the at least one intra mode from the derived listof intra modes, additional intra mode candidates.

Clause 27C. The device of clause 26C, wherein, to insert the additionalintra mode candidates, the one or more processors are configured to:insert, into the MPM list and after the at least one intra mode from thederived list of intra modes, one or more default candidates.

Clause 28C. The device of clause 26C or 27C, wherein, to construct theMPM list, the one or more processors are configured to: insert, into theMPM list and before the at least one intra mode from the derived list ofintra modes, one or more intra mode candidates that are prediction modesfrom neighboring blocks of the current block.

Clause 1D. A computer-readable storage medium storing instructions that,when executed, cause one or more processors of a video coder to performthe method of any of clauses 1C-7C.

Clause 1E. A computer-readable storage medium storing instructions that,when executed, cause one or more processors of a video coder to performthe method of any of clauses 8C-14C.

It is to be recognized that depending on the example, certain acts orevents of any of the techniques described herein can be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,not all described acts or events are necessary for the practice of thetechniques). Moreover, in certain examples, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore DSPs, general purpose microprocessors, ASICs, FPGAs, or otherequivalent integrated or discrete logic circuitry. Accordingly, theterms “processor” and “processing circuitry,” as used herein may referto any of the foregoing structures or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method of decoding video data, the methodcomprising: deriving, for a current block of video data and usingdecoder side intra mode derivation (DIMD), a list of intra modes usingreconstructed samples of neighboring blocks; constructing, for thecurrent block, a most probable mode (MPM) list, wherein constructing theMPM list comprises inserting, into the MPM list, at least one intra modefrom the derived list of intra modes; and predicting, using a candidateselected from the constructed MPM list, the current block.
 2. The methodof claim 1, further comprising: decoding, for the current block, a DIMDflag having a value that indicates whether DIMD is enabled for thecurrent block of video data, wherein deriving the list of intra modesusing DIMD comprises deriving the list of intra modes using DIMDregardless of a value of the DIMD flag.
 3. The method of claim 1,wherein inserting the at least one intra mode from the derived list ofintra modes into the MPM list comprises: inserting, into the MPM list, afirst candidate from the list of intra modes derived using DIMD; andselectively inserting, in to the MPM list, a second candidate from thelist of intra modes derived using DIMD.
 4. The method of claim 3,wherein selectively inserting the second candidate comprises selectivelyinserting, based on a sum of intensity of the second candidate from thelist of intra modes derived using DIMD, the second candidate into theMPM list.
 5. The method of claim 1, wherein constructing the MPM listfurther comprises: inserting, into the MPM list and after the at leastone intra mode from the derived list of intra modes, additional intramode candidates.
 6. The method of claim 5, wherein inserting theadditional intra mode candidates comprises: inserting, into the MPM listand after the at least one intra mode from the derived list of intramodes, one or more default candidates.
 7. The method of claim 5, whereinconstructing the MPM list further comprises: inserting, into the MPMlist and before the at least one intra mode from the derived list ofintra modes, one or more intra mode candidates that are prediction modesfrom neighboring blocks of the current block.
 8. A method of encodingvideo data, the method comprising: deriving, for a current block ofvideo data and using decoder side intra mode derivation (DIMD), a listof intra modes using reconstructed samples of neighboring blocks;constructing, for the current block, a most probable mode (MPM) list,wherein constructing the MPM list comprises inserting, into the MPMlist, at least one intra mode from the derived list of intra modes;selecting, for the current block and from the MPM list, a candidateintra mode; and encoding, for the current block, one or more syntaxelement that specify the candidate intra mode.
 9. The method of claim 8,further comprising: encoding, for the current block, a DIMD flag havinga value that indicates whether DIMD is enabled for the current block ofvideo data, wherein deriving the list of intra modes using DIMDcomprises deriving the list of intra modes using DIMD regardless of avalue of the DIMD flag.
 10. The method of claim 8, wherein inserting theat least one intra mode from the derived list of intra modes into theMPM list comprises: inserting, into the MPM list, a first candidate fromthe list of intra modes derived using DIMD; and selectively inserting,in to the MPM list, a second candidate from the list of intra modesderived using DIMD.
 11. The method of claim 10, wherein selectivelyinserting the second candidate comprises selectively inserting, based ona sum of intensity of the second candidate from the list of intra modesderived using DIMD, the second candidate into the MPM list.
 12. Themethod of claim 8, wherein constructing the MPM list further comprises:inserting, into the MPM list and after the at least one intra mode fromthe derived list of intra modes, additional intra mode candidates. 13.The method of claim 12, wherein inserting the additional intra modecandidates comprises: inserting, into the MPM list and after the atleast one intra mode from the derived list of intra modes, one or moredefault candidates.
 14. The method of claim 12, wherein constructing theMPM list further comprises: inserting, into the MPM list and before theat least one intra mode from the derived list of intra modes, one ormore intra mode candidates that are prediction modes from neighboringblocks of the current block.
 15. A device for decoding video data, thedevice comprising: a memory configured to store video data; and one ormore processors implemented in circuitry and configured to: derive, fora current block of video data and using decoder side intra modederivation (DIMD), a list of intra modes using reconstructed samples ofneighboring blocks; construct, for the current block, a most probablemode (MPM) list, wherein constructing the MPM list comprises inserting,into the MPM list, at least one intra mode from the derived list ofintra modes; and predict, using a candidate selected from theconstructed MPM list, the current block.
 16. The device of claim 15,wherein the one or more processors are further configured to: decode,for the current block, a DIMD flag having a value that indicates whetherDIMD is enabled for the current block of video data, wherein, to derivethe list of intra modes using DIMD, the one or more processors areconfigured to derive the list of intra modes using DIMD regardless of avalue of the DIMD flag.
 17. The device of claim 15, wherein, to insertthe at least one intra mode from the derived list of intra modes intothe MPM list, the one or more processors are configured to: insert, intothe MPM list, a first candidate from the list of intra modes derivedusing DIMD; and selectively insert, in to the MPM list, a secondcandidate from the list of intra modes derived using DIMD.
 18. Thedevice of claim 17, wherein, to selectively insert the second candidate,the one or more processors are configured to selectively insert, basedon a sum of intensity of the second candidate from the list of intramodes derived using DIMD, the second candidate into the MPM list. 19.The device of claim 15, wherein, to construct the MPM list, the one ormore processors are configured to: insert, into the MPM list and afterthe at least one intra mode from the derived list of intra modes,additional intra mode candidates.
 20. The device of claim 19, wherein,to insert the additional intra mode candidates, the one or moreprocessors are configured to: insert, into the MPM list and after the atleast one intra mode from the derived list of intra modes, one or moredefault candidates.
 21. The device of claim 19, wherein, to constructthe MPM list, the one or more processors are configured to: insert, intothe MPM list and before the at least one intra mode from the derivedlist of intra modes, one or more intra mode candidates that areprediction modes from neighboring blocks of the current block.
 22. Adevice for encoding video data, the device comprising: a memoryconfigured to store video data; and one or more processors implementedin circuitry and configured to: derive, for a current block of videodata and using decoder side intra mode derivation (DIMD), a list ofintra modes using reconstructed samples of neighboring blocks;construct, for the current block, a most probable mode (MPM) list,wherein constructing the MPM list comprises inserting, into the MPMlist, at least one intra mode from the derived list of intra modes;select, for the current block and from the MPM list, a candidate intramode; and encode, for the current block, one or more syntax element thatspecify the candidate intra mode.
 23. The device of claim 22, whereinthe one or more processors are further configured to: encode, for thecurrent block, a DIMD flag having a value that indicates whether DIMD isenabled for the current block of video data, wherein, to derive the listof intra modes using DIMD, the one or more processors are configured toderive the list of intra modes using DIMD regardless of a value of theDIMD flag.
 24. The device of claim 22, wherein, to insert the at leastone intra mode from the derived list of intra modes into the MPM list,the one or more processors are configured to: insert, into the MPM list,a first candidate from the list of intra modes derived using DIMD; andselectively insert, in to the MPM list, a second candidate from the listof intra modes derived using DIMD.
 25. The device of claim 24, wherein,to selectively insert the second candidate, the one or more processorsare configured to selectively insert, based on a sum of intensity of thesecond candidate from the list of intra modes derived using DIMD, thesecond candidate into the MPM list.
 26. The device of claim 22, wherein,to construct the MPM list, the one or more processors are configured to:insert, into the MPM list and after the at least one intra mode from thederived list of intra modes, additional intra mode candidates.
 27. Thedevice of claim 26, wherein, to insert the additional intra modecandidates, the one or more processors are configured to: insert, intothe MPM list and after the at least one intra mode from the derived listof intra modes, one or more default candidates.
 28. The device of claim26, wherein, to construct the MPM list, the one or more processors areconfigured to: insert, into the MPM list and before the at least oneintra mode from the derived list of intra modes, one or more intra modecandidates that are prediction modes from neighboring blocks of thecurrent block.